It varies. Apple don't specify a particular vendor and model.
What's that got to do with being savagely gouged on price?You're forgetting that the average apple user really couldn't care less about model - just that it does the job.
They should do for the ridiculous amounts they charge. To upgrade from the default 640gb to 1gb drive when buying a mac pro costs £80. You could buy a second 1tb for less than that.
What's that got to do with being savagely gouged on price?
Buy a second drive then. It won't affect your warranty.