Oh, sorry. Yeah I meant why they end up producing buggy software when competitors like Apple have proven it's possible to both ship and make stable software. And Apple does both hardware and software.
You partly answered your own question. When you control the hardware and the software, the number of testing variables goes down dramatically.
Of course, by that logic, since the same company that made my macbook did the hardware and the software, I'd expect it to be much more stable than my windows boxes, but sadly it is not.
Windows 7 crashes on me about as often as OS X (or Ubuntu for that matter). Visual studio on the whole seems less buggy than XCode. iTunes is bit of a monstrosity and seems to bug out on fairly regular occasions. And while I haven't had any problems myself, I know of several people who have had lots of trouble with wifi on their MBAs. Where you thinking of any specific examples?
As much as I like bashing Microsoft (and they do make buggy software), this is not an apples to apples comparison - Apple has much more control over the complete stack than Microsoft does. And Apple software is hardly perfect either.
What Apple (Jobs, really) did was always rehearse every keynote to exhaustion (his and everyone else's), until everything is absolutely perfect. Not everyone is as perfectionist as Jobs was.
I had IIS blue-screen on me in front of a full audience (yes, I once worked for the evil empire). And I did rehearse the damn thing a good couple times.
The difference with Apple is, Apple has one use case for their software. There is plenty of blogging on HN every week with someone complaining that OSX is unstable or unsuitable for a use case outside of what Apple had intended.
Apple controls the hardware, the software, and the user. This makes it a lot easier to appear bug-free.
Honestly? The average consumer doesn't need that degree of quality. I have friends who cannot tell the difference between scrolling on my Android phone and scrolling on my iPhone. It's something that drives me wild.
I feel that it's almost the same principle - things may crash here and there but it's "no big deal" to most people.
Are you actually suggesting that iTunes is "stable software"? Please wake me up when your fantasy is over. Also, I've experienced more crashes within iOS on my iPad than I have in 15+ years of using Windows. Anecdotal evidence of course but it's not like you cited any actual data either.
Of course, by that logic, since the same company that made my macbook did the hardware and the software, I'd expect it to be much more stable than my windows boxes, but sadly it is not.