Rock Band is actually going through a similar issue right now. Harmonix only licensed the DLC songs for 5 years, so over the past year we've lost a few songs from the store. You keep the songs and can redownload if you bought them, but once they're off the store, they can't be purchased by any new users.
They are actively relicensing the vast majority of them though.
This just hasn't happened much before due to games mostly being released at retail, so terms are always on retail timescales. Licensing doesn't really account for the infinite supply of digital releases quite yet.
edit: there were also a couple of DLC and disc-export songs you couldn't play in Rock Band 3 because of licensing or Guitar Hero signed exclusivity rights. So for example, you could export Dani California from Rock Band 1 to play in Rock Band 2. Then right before Rock Band 3 came out, Activision was working on a RHCP GH game, and got exclusive rights. Rock Band 3 wouldn't load Dani California. When Guitar Hero died, Harmonix was able to patch RB3 to finally load the song.
/rockbandtangent
So in theory, PA is limited by the length of the term, and if anyone snatches exclusive rights to a table after they've had it, which means if they made a Pinball Arcade 2, they'd probably have to block the table from loading if they were doing the Rock Band thing.