... just slap on a "no warranty/support if used on 3rd party hardware", and the hackers would be happy.
But that is the point of Apple's marketing strategy - they are selling cut price hardware at huge markup prices and they don't want to open the floodgates to nerds with apple clones and cut their market share.
Now that they have moved to Intel hardware and nVidia graphics they basically sell the same boxes as everyone else (except for a bit of prettifying) so opening the market (even without support) to MacOS on anything other than an Apple produced computer would kill their market.
The same could be said for iTunes - why not give the option of unprotected MP3 files and alongside Apple's restrictive formats and open the iTunes shop to non-iPod users. Simple the market share of iPods would drop like a stone and that is the major revenue stream.
Apple have always had one strategy (right back from the first Apple computers but especially since the Mac was introduced in the early 80s):
1) Say Mac is better than DOS/Windows/Linux/any other OS very loudly and continuously in a mantra like way until their own customers become brainwashed and would never consider moving to a different computer system
2) Lock the OS to their own hardware and only their hardware
3) Hike the prices - it must be good because it is so expensive
4) Put it in packaging that is so minimalist it must be cool
5) Repeat every year with pretty much the same products but more expensive with a few tweaks and persuade customers they can't live without the next shiny toy
Its a clever revenue model - but release software products into the wild west of PC land and the model would break instantly. For a start they could no longer say that Apple computers are better than anything else because everything else can run MacOS.
Its the same old story and one of the reasons they are locking down application development for iPhones and bricking devices that break out of the Apple way of doing things.