The experience isn't going to be radically different for the Apple user after this. There will be some adjustment, some tweaks here and there, but it is not going to be a dramatically different experience.
It represents a big win for Apple and the Mac platform. But Apple doesn't represent a threat to AOL's business. Apple isn't a media company; it's not in online services. It's not the same threat as when Microsoft wanted interoperability.
I don't think Microsoft plans on ceding this market to Apple or anyone else at this point in time. What that means in terms of tactical solutions, it's too early to tell. They're probably considering any number of different options.
How seamless does that mechanism need to be under this law? The devil here is in the detail. It's quite possible that Apple says they're in compliance with this law. No one is locked into Apple's music format.