Why do you think you are contributing to Apple? It's common knowledge that Apple subsidizes their OS development with hardware profits. You are cheating Apple out of these profits. If this practice continues, Apple will start charging for the OS what it really costs to develop it and be forced to put in "features" like product activation and DRM.
"Common knowledge"? Did you make that up?
I am certain that Apple makes back all development work on the OS from individual sales to consumers. At $129 each, every 2 years, and tens of millions of Mac owners, and the high uptake rate, Apple makes hundreds of millions of dollars in revenue from OS sales alone. Never mind the portion of every bit of hardware that is counted as income towards OS development, third party licensing, software patent income, and so on.
By cheating Apple out of profits, they will be forced to add activation and raise the price of MacOS X by hundreds of dollars (look at the price of Vista Ultimate and then consider the size of the Mac market vs. the PC market). Then we'll all be cheated.
Microsoft like to make 80%+ margins on their products. Vista is a complete rip off for what you get. Remember that it was also their first consumer OS release for 6 years, so they're covering 3x as much development time, and probably a whole load more developers.