The why is obvious. The wooden back makes the keyboard a "look at me I'm beautiful"-OH, just like shiny golden iPhones. The phone will already by thick enough to be noticed by many people, I don't want to attract their remarks and questions more than that. I don't want a luxury phone, just a useful and discrete one with as much open source and Linux chunks as possible inside.

There will be two groups of customers of course, those who want a beautiful keyboard, and those who want a keyboard on a "don't look at me, I'm normal"-phone. Both are right, both are wrong!

Perhaps it will change the price too, but I don't know it yet so that's not the decisive part for me. And anyway, it's too early apparently, just answering to the "why?" and seconding that wood-less keyboards would be cool.