There must be something about the new OS that provides more value to Apple than the fee they might have charged. The paranoid part of me is apprehensive about that.
I think that's more along the lines of they figured out a better way to do the accounting.
Just recently the guidelines changed which meant that Apple didn't need to account for all revenue from iPhone over 2 years (service period) due to there being value in the software updates that would be delivered during that time; that resulted in restatement of income and presumably eased the issue with delivering updates for non-subscription devices free of charge.