When the people who have done the research on the issue all come back with the same conclusion (which is "based on the way that Apple decided to book the revenue for iPod touches, any update that adds major new functionality must be sold for a fee, per GAAP guidelines"), the only thing that seems questionable is Apple's initial decision on how to book iPod touch revenues, and even then, that's not clear cut as it seems that their position when the touch was first launched was that they were NOT going to update it ever to run third-party native apps. (i.e. the iPod touch would never be receiving updates containing major new functionality, nor would it ever have feature parity with the almighty iPhone). It wasn't until about three months of major uproar from consumers AFTER that decision that Apple did a complete 180 on their stand (on both the touch and the iPhone).
Again, what's to question? Based on the analyst reviews of the issue I've seen, Apple cannot undo the decision that resulted in them charging for iPod touch upgrades.
I think the main reason that Apple does not use subscription accounting for the iPod touch is that investors would see a massive decline in iPod revenues in the short term. A large percentage of investors are extremely reactionary, and (prodded on by people like Jim Cramer on CNBC) would not bother to investigate the logical reason for the decline. They would just freak out.