Either you want to run under Linux or you want to run under Windows.
Dual booting isn't really the answer because it contributes to the network effect for Windows. A purchase for Windows is a vote for that OS to continue to get versions explicitly for it.
WINE's not any better an answer for those already on Linux for a while- and for the same reasoning.
The price is what each publisher set (not the studio) based on what return on their investment of a production run of a given size would be- if you like the game, but don't like the price, don't buy. But don't be whining when you don't have ANY other titles because they don't have metrics to us to make Linux versions. A purchase of a Windows SKU is a vote for THAT OS with your dollars as far as the publisher is concerned. They typically don't look at "installed user base" of an OS except to contemplate a possible version. Things not selling won't help us, never mind the pricing (they WILL NOT look at what the Linux SKU cost to get- they will only look at numbers sold and base it off of that...). If you want to play ON Linux, you need to BUY Linux.
As it stands, most of everyone will be unfamiliar with the MacOS gaming situation. Pricing is very similar to what you're seeing here in many cases. They buy all the same. They don't bitch about the Windows version being cheaper or in the bargain bin before it comes out. They don't typically buy up a "gaming rig" just to run Windows so they can play those games. They buy the stuff because they know if they like it and they buy it, there'll be more down the line- and better fare.
Think of the price delta right at the moment as the premium to NOT have things like Vista on your machine, if you have to. Sure, you can run XP now, but what happens when they don't activate anymore? What happens when they completely turn the lights off on things like they're doing with "Plays for Sure"?? If you can't justfy the expense, it's okay. If you don't like it, it's okay. If you can swing both, buy it and don't bitch about the price difference, okay?