The intent is to allow companies time to implement the change. But if you'll pardon my cynicism, in practice, what ends up happening is companies just use it as a tactic to delay the implementation and continue recording the revenue.
At the very least they should forfeit the revenue that they earn during the period for this. I'm not sure exactly how the fines work and whether they take this into account, but I doubt Apple is seriously going to use the 12-month period to actually come clean and change their ways. I think they'll just use it as more time to come up with some new bullshit form of non-compliance.