I became a Mac user about a year and a half ago after abhorring them myself (for many of the same reasons), but once I sat down and actually used one for a bit (about 3 hours) I fell completely in love. As to the way I usually deal with the exact same complaints:
"I can't play games on them." - Maybe not as well or as many as on a PC, but this just isn't a PC and it wasn't intended for gaming but as for "can't", you're just plain wrong. The PC vs Mac gaming discussion is the same thing as XBox vs PlayStation, franchises choose certain platforms to release their product on.
"They cost too much." - I feel they cost as much as a computer should cost. The only reason they are more expensive than most PCs is because they never got in bed with advertisers which helped to subsidize the price a user has to pay for their machine. Besides, when you account for things like doing audio recording and how many times easier it is on a Mac vs a Windows machine, the price becomes more than justified. Besides, when you compare things like Dell's XPS lineup and the new Surface Laptop you'd be paying basically the same price anyway.
"I like to upgrade my computer, and be able to fix it if something breaks." - This one I agree on, I have no argument in Mac's favor on this point.
"They're underpowered. I don't wanna pay that much money to get a computer with those specs." - What? How are they underpowered? Compared to what? Show me any 2011-era Windows PC that performs anywhere near as well as my 2011 Air does.
Yes, there is a premium price to pay for using an Apple product, but ultimate user freedom aside, I feel they are more than worth the price.
Definitely, I think you summed up the gaming thing better than I did. But that last argument I usually get from people who work in the video editing profession, comparing the pure specs of a machine instead of its true benchmarking performance. But like I said, it's very easy to replace components on a Mac. At least, most of them-- You still can't really swap out the motherboard or CPU, but I guess those are things that are seldom changed anyways.