The interview deals specifically with Gruber’s opinions on the OS X GUI. Interesting stuff, esp. some of the info about the original Aqua demos.
I believe Jobs is mostly responsible for Apple’s almost-entirely-arbitrary use of brushed metal windows. E.g. the decision to use brushed metal in Safari. I could be wrong – I have no sources or evidence to back that up. But my thinking is that Jobs sees the “consistency,” so to say, as stemming from his own aesthetic judgement. That’s Jobs’s gift: his taste, and his ability to motivate teams to meet his standards. So if he feels in his gut that, for example, Safari looks better with brushed metal windows, then he knows he’s right, and that’s the end of the debate. It doesn’t matter if the answer contradicts the Mac OS X Human Interface Guidelines.