The argument isn't that one _could_ dremel Debian, in fact, after recently installing KDE on a new machine I'd argue that one _has to_ dremel it a bit to get a good UX. The argument is that the Mac - for all its flaws - has a better UX.
People who care about UX will gravitate towards the Mac. A subset of these folks start developing software, as a consequence, the people creating Mac GUIs do better UX than those using and developing for Linux.
Yeah, you see that's where I don't think it's "people who care about UX" who gravitate to Mac. Maybe 10 years ago, sure, when Apple font rendering was massively superior to anything else on the market and people would put up with endless crap with the corporate monster in order to not see ugly fonts. But these days, I'm not so sure.
The people who actually really care about UX want to dremel their stuff because the little tiny discrepencies annoy them (like you).
The people who flock to Mac these days are plain consumers. They want to be protected from the intricacies, have something that "looks good" without having to decide what "looking good" actually involves, or making any decisions about it. The average Mac user these days sees Apple as a brand that says something about their good taste.
and yes, I completely agree that you have to dremel your Linux install to get it looking good. But that's half the fun :)
People who care about UX will gravitate towards the Mac. A subset of these folks start developing software, as a consequence, the people creating Mac GUIs do better UX than those using and developing for Linux.