Didn't you concede as much when you said "it is inherently obvious that OS's with greater numbers of users will exercise a greater number of lines of code?" I thought that was the point you were making when you said "My complaint is that few Mac and Linux users seem to be aware of simple engineering dynamics," implying that the reason those OS's used less code is that they have less users.
Anyway, it''s my understanding that MS code bloat is pretty common knowledge. It's something I've run across a number of times, though I can't cite a specific source at the moment. David Pogue, maybe?
I've got a buddy up in Redmond at MS, and this is one of our general understandings when we're comparing Mac apples vs Windows oranges. 10 gigs on a Mac hard drive goes farther to do the same thing than 10 gigs on a Wintel machine, because of the extra code necessary. (We're talking pre-OS X and pre-XP, anyway). Same with the mHz on the processors... a 500 mHz G-4 is faster than a 500 mHz Pentium III, for example. Granted, Wintel machines make up for this by offering bigger hard drives and processors with more mHz than Macs, so those sorts of things tend to balance out.
...if the Mac OS uses a proprietary chip (for QuickDraw or whatever other GUI components it uses), that would reduce the code footprint required in dynamic RAM; however, the fact that code resides in a proprietary chip doesn't mean that it doesn't exist; it is part of the operating system and has to be included as part of what you would call its "bloat".
That's kind of a technicality. The bottom line is that the code isn't in the software, and that's where the recent XP glitches are showing up, no?