Note: This is a paraphrasing of a quick forum post I'd written when the 8X was originally announced. As such, it's slightly outdated and a little sloppy, but I still hope it provokes some deliberation about the designs of these phones.
The development of the Windows Phone platform has resulted in some of the most unique looking phones to come along in some time. The Nokia Lumia series and the HTC 8X both forgo the typical aluminum and/or black plastic construction of their competitors for an array of vibrant, polycarbonate devices. The designs are, at a glance, similar: Matte finish. Bold, uniform color. Soft edges. Curved display. So similar, in fact, that upon the announcement of the 8X, crowds of commenters across tech blogs denounced it as being a shrewd rip-off of the Nokia line. But I don't think so.
I believe these similarities are primarily coincidence, and actually commend HTC for following this direction despite an apparent resemblance. I feel the designs of the two companies evolved from different sources and happen to be converging at mutual point in time, for a mutual software backbone. Any likeness of the 8X and 8S to the Lumias doesn't come from an attempt to copy Nokia’s design, but rather from an aesthetic that is inherent in HTC's desire to physically match the design language of Metro. In other words, if I had never seen a Lumia phone and were attempting to design a product inspired by Metro, I think there's a good chance I'd come up with something similar.
(Yes Metro, dagnabbit. Modern UI sounds horrendously bland.)
Matching the Software's Design Language:
Microsoft's current design philosophy is about being "authentically digital": getting rid of fake textures, cheesy skeumorphism, unnecessary glossiness, etc. It features bold, solid colors, simple transitions, and squares. Lots of squares.
The 8X (and 8S, to a slightly lesser extent) seems to aim for precisely that. Making the phone's hardware feature patterns or textures, a la Samsung or Motorola, would immediately detract from and clash with Metro's design. And since gloss is to Metro like open-source is to Apple, a matte finish makes the most sense.
Unibody polycarbonate helps maintain the uniformity of structure, color, and texture. Metal construction would interrupt the design, as it would necessitate a plastic or glass part to the back of the device for the antennae to function properly (see One S, iPhone 1 and 5, etc).
Authentically Digital, but Authentically HTC:
But it's not just Metro that HTC is taking cues from; the 8X is also evolved from their very own Android flagship, the One X. This is a phone which already features unibody polycarbonate with a matte texture, as well as a curved display. Having a similar construction connects the two phones aesthetically, and the signature HTC grilles are visibly present and highlighted by color on the new devices. To me, the 8X largely resembles a One X repurposed for Windows Phone.
So if it wanted to be so "Metro", why did HTC chose to taper the design instead of just making a plain rectangular prism? For one, a curved screen makes it easier to use WP's frequent side-swiping. Then, well, there's issue that people actually have to hold these things, and a tapered design is simply more comfortable. This is especially true with larger screen sizes, where more reaching means more uncomfortable pressure on the palm. It also has the nice side-effect of making the phones look and feel thinner than they are. I mean the iPhone 4S looks nice, but it sure doesn't feel as nice to hold as my tapered One S. In any case, the tapering is quite different from the Nokias, which are more cylindrical.
And so, just that short train of thought leaves us with a phone that comes in solid colors, a square shape, matte texture, tapered edges, curved display, and polycarbonate construction.
A Different Source, a Similar Destination
Nokia's design, on the other hand, evolved from a completely different direction, and somewhat coincidentally. Its current design language can be traced all the way back to at least the Symbian N8, going N8→N9→Lumia 800→Lumia 900→Lumia 920.
The MeeGo-running N9 followed the N8, and is basically identical to the subsequent WP7 Lumia 800, which defines what people identify as the "Nokia Look". It just so happened that the N9/800 solid-colored and seamless construction seemed to fit Windows Phone quite well.
As such, I don't think the Nokia phones were designed solely with Windows Phone in mind, because their aesthetic started long before WP7's release. With HTC, other than some cues from the One X, its design seems to have evolved for the specific purpose of application to Windows Phone 8.
The unknown variable here is just how long ago Nokia knew they'd be running Windows Phone. Was the N9 redesigned to further match Metro because of prior knowledge that the hardware would be re-applied as a Windows Phone device? I've seen conflicting information on this, and watching the design videos for both the N9 and Lumia 800 only further muddles the matter. But if it was, I don't think it played a such a dire role given many of the elements already present in the N8 and other previous Nokia phones.
A Windows Phone Family
At the end of the day, whatever the reasons may be, HTC and Nokia's related aesthetics are a good thing for Windows Phone as a whole. As the products of the two main players in the market, these designs give WP8 readily identifiable visual character, in the same way you can identify an an Apple product at a glance, or you used to be able to identify Android HTCs by their chin.
I also completely think it's possible Microsoft had a significant influence in HTC's design process, as they might have had for the Lumias, and tried to direct them towards the colorful styling in order to strengthen brand presence for the OS (and knew Samsung probably didn't care, since they are so successful on Android). It should be noted, however, Nokia has started to shift gears a bit. It's transitioned towards a glossy sheen (ugh), which will help differentiate the companies' products at the store stands.
Personally, I expect HTC to do quite well with this new lines of phones, probably better than Nokia, simply because I believe the designs are more universally attractive than those of the new Lumias. As nice as the Lumia 920 and 820 are, people are growing tired of gloss. Then they'll see the HTC's that have similar functionality, but cleaner designs. And blue.
Then there's the issue that Nokia has previously shown more carrier exclusivity than HTC has. If they continue to have their flagship available on AT&T only, their potential US sales will be greatly diminished. Besides, it's not as if HTC is a newcomer, it already has a strong following of its own.
But we'll see. Whichever way things go, I think the outlook is better than ever for the Windows Phone ecosystem. I might just move away from the Android Army.