Well thought out but I need to disagree with a couple of points.
In a nutshell, if you are really into computers ... Linux by a mile. If you want a no fuss tool ... MAC by a mile. If you play games, or don't know a dishwasher from a computer ... Windows.
By any reasonable standard I would qualify as "really into computers" and I use all of the above professionally plus a bunch of other systems. Apple's OS X has UNIX (well BSD) underpinnings and is great for people who are "into computers". Heck most of the OS (but not the GUIs or the critical APIs) are even available as open source. If it is a available in Linux the odds are you can make it run on a Mac.
Also
MAC's are for people who have enough upfront money to buy something that generally works, and works well, and doesn't break much.
The $ thing is always tough. Recent cost comparisons of equivalent systems show that Apple is usually about the same cost (and often lower) as other brands. The challenge is in the whole equivalent systems thing and a reputation for being high priced. Apple does not have products available to address every possible market segment and generally isn't that interested very low end machines. The sheer variety of PC systems out there means you can almost always find a lower cost system but an honest comparison of capabilities will show you why it costs less. If you don't need those features / capabilities - great but that doesn't make the Mac high priced - just configured in a non-optimal way for your needs.
By the way - thanks to all for keeping this a well reasoned discussion. In the end a computer (any computer) is just a tool (well a toolset). Find what works for you and use it well.
- Eric