Having just (involuntarily) switched to a Mac at work, I can also attest to the fact that Mac users tend towards impulse buying software... The fact that I have to buy software to get proper window management and a good window switcher makes me furious. App-only switching makes no sense to me. I just want to pull up the last window I was looking at, I don't want to have to think about whether it was in the current app group or not. Also, not allowing that to be customized makes no sense. The OS has all of the info needed, and the market for 3rd party apps shows there is a desire... but I guess I'm just 'holding it wrong'.
Most people in the office have spent $100 on software that just customizes the OS, not even considering the other dev tools that they purchase.
As much as I detest OS X, IF I were releasing desktop software for-pay, I would focus on OS X ($ per user) and Windows (kids & college students).