Devin at The Nokia Guide is the source for the video embedded here, as well as the transcriber of the most interesting parts, some of which are quoted below.
From Devin's summary:
When asked how they were able to deliver the Lumia 800 that fast, Pannenbecker mentions several reasons: Doing less things, but execute them better, focusing on the right things, to deliver faster and they build on something “somewhat mature, not finished” referring to the N9. This also means that Nokia does consider the Lumia 800 as a “version 2.0” if you will of the N9 and not just an N9 with a new operating system as many seem to suggest. He mentions 4 principles that would define the N9 and the Lumia 800: Clear, Refined, Human and Advanced....
Nokia has been talking a lot about how both the N9 and the Lumia 800 fuse software and the hardware. I tend to agree with this. On previous Symbian devices for example, software always somehow managed to lag behind the solid Nokia hardware. In this case he mentions how the Metro UI’s square tiles and soft internal match the rectangular footprint of the Lumia 800. Perhaps this also affected Nokia’s reason not to go Android? Perhaps it wasn’t just about differentiation, but also the fact they were pushing “hardware should match software” and Windows Phone clearly does that.
The two products were also about refinement in the sense that they wanted to improve antenna performance, which he says is kind of a black magic, never a sure thing and very difficult to do. That’s why they decided to use Polycarbonate, basically a type of plastic and one allows for great reception. Even if it’s plastic, they also decide to do things differently, treating it as if it was a premium material and precision milling the speaker grille for example. The final product and I think you will agree, doesn’t look and feel like plastic at all. One could almost be fooled into thinking that it’s some kind of brushed aluminum.