I think they quickly realized that, but it took them a while to create an aluminum iPhone the right way, because as we know aluminum is not great for radio connections, so you'll have to arrange the radios in such a way that the body doesn't interfere with them, which is probably why it took them so long, and why they made the iPhone 4S identical to iPhone 4.
I won't even discuss Samsung, which seems to have a fetish for crappy plastic. If it were after me, phones would all have metallic bodies, because it feels the best in hand, but you won't get full metal bodies anyway, but a mixture of metal and plastic or glass (like iPhone 5).
The best compromise between being easy to make and also feeling solid in hand seems to be polycarbonate right now, and more manufacturers should be using it, along with more colors for their devices, as I'm getting really bored with the black and white "options". It's like most of them are afraid to even try other (bold) colors, and just want to appeal to the lowest common denominator, and in the same time complain about not being able to differentiate, other than changing the skin on Android, which I think it's just an easy way out for them, instead of actually doing interesting things with their hardware design.
The same thing applies to Nokia, which in the past have said that they wouldn't be able to differentiate with Android, but I think a Lumia-like device would've sold a lot more units with Android. Nokia's growth is being limited a lot by WP's own growth right now. They can only grow as fast as WP is growing, and if anything, it's Nokia pulling WP after them, rather than the other way around, which just goes to show how much better it would do with Android, which doesn't need to be "sold" to the public anymore.