sometimes designers do different mediums to get different ideas - different results - different moods. Just by switching the mediums that your used to can change your whole perception on design in general or that particular design.
look at the facelifted e90 330i and perhaps the Ford GT sketches.

i would assume they're wearing suits because of the grand opening of the new GM design center plus hes got a spiffy " drank " to quench his thirst. i wouldnt think they would like gettin the designers drunk and workin with the supplies. however that could be the motives over at GM.