Probably because the dev device will be the first to be shown. And since this will cause lots of headlines and interest in the tech media then why not present it in an attractive way and get some nice publicity?

I don't buy it. I just watched the teaser again 3 times. Each shot at the beginning represents a 'sense', ear=earpiece, eye=camera etc. Fingers sliding across water and ice=touchscreen gestures, and shot of keyboard with fingers playing water like a piano...too elegant and obvious just for developers.
Then later after the blowing, a longer shot of the keyboard in all its glory.

I'm still not convinced the end product will be touch only. Sorry.