Closed System Design

I was discussing computer platforms with someone the other day when a discussion of Apple vs. Dell came up. One of the arguments that was made was how well functioning the Apple system was compared to a WinTel OEM system.
Of course he was right, but there is more to the story. Apple (and Sun, and other Unix/Mainframe vendors) is a closed system. The same vendor makes the hardware and software for the platform, or selects a very limited list of hardware that will integrate into the platform. With this reduction of “options” the software that is deployed onto the system will no doubt function better.
It’s the old “do one thing really good, or lots of things okay” approach. As I watch the Linux kernel mature I wonder the same thing. Will there be a point where the system is attempting to be soo broad base that it isn’t great at any one thing? So far this hasn’t been the case… I would imagine it is a hard pitfall to avoid.