Apple doesn't want to expand. They are happy with their place in the world. They build a great little computer system. And it is a system. You cannot separate the machine from the OS, they are like a hand in a glove. Yeah, you can load nearly anything into nearly anything else but its the symbiosis of the machine and OS that makes Apples what they are. The primary reason they work as well as they do is because they only support Apple peripherals (well, there are others but in those cases, its the peripherals that have included compatiblity into their products not the other way around). The MacIntosh line started when Steve Jobs was given a presentation by the folks at PARC back in 1979 on WIMP (Windows, Icons, Menus, Pointers). They tried to do it themselves with the LISA computer but it had problems. Finally, Jobs hired some of the PARC staff and the result was the Mac. Its still the same language (a derivative of SmallTalk 80) though greatly evolved. The basic concept was to develope a very tight system with the hardware doing as much of the work as possible, that meant the hardware had to be very compatible. That limits flexibility. It also means there can't be a lot of messing around with the OS by the users. So, Apple doesn't care. They make the machines they make and their users love them. What could be better. MicroSoft/Intel/IBM went the other way, the everything works with everything, market share is priority, "we must conquer the world" mentality. Their users are generally unhappy, because although MS is very flexible, to be so requires it be massive and that means there's lots and lots of problems. In Windows, the software does the lion's share of the work, the machines are just platforms. So you have Apple OS of what, maybe 40 MB versus Windows with 200 MB. Right there you see a big performance difference. There's 160 MB of RAM that can be used for doing work rather than managing hardward and plugging holes and keeping out the demons.
Don't get me wrong, I use Windows, mostly because I use AutoCAD and its no longer available in Apple. Plus I like to muck about with my machines. I like to take them apart and see if I can make them better. That is a cardinal no-no with Apple. You take what you get. Period. The company will decide what's good and what's not and you just stick to your work. In the end, that attitude is what I don't like about Apple. You often think of Apple as the rebels and the MS/IBM/Intel combine as the big empire controlling everything. Not so, Apple is the most controlled system out there, you do it their way or you don't do it. On the other hand, the MS/Intel paradigm is total chaos. You can do anything you want.
There's pros and cons to both sides. But that's the point, there are not sides, just different faces. Apple does what they do and they do it well. They don't want to be MS/Intel. Funniest thing is that the old divide was Apple versus IBM (with MS-DOS) and now IBM makes the chips for Apple, they are best buds.