Though that's the only page so far I've found with a dark black background. I'm not sure why it's black, all the other Macbook Air pages have a light background.
This is the old and unchanged MacBook Air page. Apple heavily customizes product pages – no two look alike. That has always been the case and is definitely nothing new. I think that the Final Cut Studio page was entirely black in the past, maybe even the Mac Pro page.
Obviously. Site wide elements obviously changed (I think the site map at the bottom also slightly changed), but that’s not really relevant to the comment. The page content itself – everything minus the site wide elements – is completely unchanged. It being black is not new and also not surprising.
Honestly if there's a difference from the old version I don't see it myself.