I don't really buy the argument of "everyone uses it, so supporting it is easier" thinking, nor should such a statement preclude using something else. After all, you yourself use a G1 instead of the iPhone, Blackberry, or Windows Mobile phone. Sure, your chances of finding someone random to help with a particular problem might be a bit higher with Windows, but Apple does offer excellent support via the phone, online, or in their stores. And since Apple makes the OS and the hardware, you avoid the support loop between the OEMs and Microsoft. Linux, I can't comment on the desktop side, but I've never had any issues getting support with Gentoo or CentOS issues online.

It also depends on what support you need. With Windows, Mac or Linux, it may be "How do I do this operation?". Windows adds on fun ones like "How do I remove all this spyware?", or "what antivirus solution do I need to make my computer run slower and maybe protect it?". And then there is the "I bought some cheap no name computer and it failed, and it only came with a 90 day warranty, how do I get my data off onto my next cheep PC?"

The amount of time I have spent supporting family and friends on computers has gone dramatically down ever since they moved to a Mac. And they aren't going elsewhere for support either, it's just that their need for support has dropped dramatically. The printer no longer stops sharing for no good reason, the system never gets infected with crap, the virus scanner updates are no longer an issue, and the hardware is lasting far longer. I even went to the extreme of recommending Apple routers or time capsules, and internet problems have also gone away with at most a power cycle required.