It's exceptionally difficult to argue the case that Apple aren't
favouring UI polish over actual working functionality, given that both
of their last two OS releases have shipped alongside a practically zero
day critical data loss bug announcment.
Playing devil's advocate, you could argue that Snow Leopard didn't change much in the UI and has a new threading API as one of its main features, showing that they're not putting the UI above all else. You could also point out the known data-loss bug that shipped in Windows Home Server and wasn't patched until a year later.
(FWIW, the Guest user thing in Snow Leopard turns out to not lose data; it just hides it. I guess that's still data loss if you don't realise the data is there and how to get it, though.)
More generally... I'm not a fan of Apple -- far from it -- and there are definitely cases where they put appearance above substance, lie in marketing, behave anti-competitively, release software with nasty bugs (who doesn't?) and do other dumb/annoying things. Which large, successful companies haven't done that on the way to where they are, though?
IMO, Apple's success, like Microsoft's, is as much to do with the ineptitude of their competitors as it is to do with anything good or bad they did themselves. Having found success/power, Apple now seem to be abusing it like Microsoft did earlier in life, which is a shame, but not unusual.
It's good to call Apple on their behaviour since they (like Google, for that matter) still somehow have the image of being a wonderful charity that produces things for the benefit of humanity when, really, they're just another big company hell-bent on making money and gaining market share. Those companies can still make good products, though, and are full of clever, well-meaning people who are often doing it for the love of what they produce and not for money; but to the companies all that stuff is just a side-effect -- a "neccessary good" -- on the path to making money. 
So, yeah, what bugs me about Apple isn't so much that they're big business (or that I'm virtually forced to buy & use their products if I want a decent DAP because the rest of the market failed so badly); it's that reality-distortion field around the company that stops people seeing what they are.