More likely the oils from your hands vs. variability from factory finishes.
Yeah, I'm sure it is. I just wonder if anything can be done about it. My particular machine seems to be a bit of a dud ($4k dud, but a dud); I'm on my third screen, already had a command-key replaced, and the deteriorating finish. I've been using Apple computers since the 90s and I'd say this is definitely my worst experience so far. (I did have a "Quicksilver" G4 733 that was kinda garbage, but only because it was dead slow! The build quality was excellent.)