You're missing that $240/year isn't your only option. Let's say I'm writing a cross platform library/server/non-gui app. I'm developing it in Linux, and regularly testing it on FreeBSD and Windows, all of which I can boot into from my main computer. Being a able to pay a few bucks every release to make sure it compiles and runs on OS X as well would be well worth it, and depending on your release schedule would probably end up costing less $50/year.