They spend a lot on R&D, and they actually innovate quite a bit. I think Apple is more trendy right now and that is the reason they're making so much money with little investment. They're investing more into advertising, branding, and image than they are into technology. It seems that Microsoft is making a little more effort to do this these days, but it will be difficult for them to totally turn things around in this respect.
In terms of technology and innovation though, Apple takes what it can from open source, and contributes back exactly as much as they're legally obligated to. They didn't design the operating system, and a lot of their original system APIs come from the NeXTStep heritage (and thus are implemented in Objective-C, which is not hugely popular but was probably the fastest way for them to take NeXT's stuff and start selling it).
This isn't really accurate. You do realize that the list of original inventions by Apple is huge. Those of us who have been using Apple stuff since the early 80s really appreciate this in a way that someone who started paying attention to Apple recently can't. In fact in the 90s, Apple was teeming with great "Apple first" technology, but nobody knew about it or used it because they couldn't market it effectively. Newton anyone?
In fact, the long running joke is that Apple *is* MS R&D dept.
Apple does use and contribute to OSS, but thats honestly the whole point of OSS. You can't knock them for that. As far as them not inventing the technology in OSX, thats not correct either. Its not like OSX was available in the OSS community and they just put it in a box. They have spent years developing the technology that sets OSX apart from other UNIX based systems. Quicktime, Core Audio, Quartz, the whole OSX GUI, the search technology that is now Spotlight, etc.. And even the tech they got from NeXT technically is "Apple" because Apple bought NeXT and all of their employees and IP. So the Mach kernel, Cocoa, WebObjects, etc.. are all now "Apple". OSX is a mixture of original "Apple" and "NeXT", but its all Apple now, and there is nothing else quite like it on the market...
Just because Apple is "trendy" now doesn't mean they aren't and haven't been innovative. These things aren't mutually exclusive. And in fact, you'd want the most innovative companies to be the most popular. Its a shame it doesn't happen that way more often.