Since Amazon had a sale ending on 10/27 offering the Win8 Pro upgrade (including DVDs) for $38.88 (well, $68.88 including a $30 Amazon gift certificate, but it just isn't Christmas unless we blow $30 somewhere on Amazon) vs. Microsoft's $39.99 download (without DVDs) I ordered one, and it arrived a couple of days ago. Just for fun I compared its 32-bit version with the version I downloaded from Microsoft and was a bit surprised to find differences - file dates a few hours apart, and nearly half a gigabyte difference in total size (most of which is the difference between install.esd on the downloaded version and install.wim on Amazon's; I'm guessing that this reflects differences in compression given that space on the DVD is effectively free at least as long as you've got enough and the difference in installation time is negligible).

I find this more curious than alarming, but thought I'd mention it in case anyone else encountered it or happened to know why it exists.