The obvious answer being that Prince of Persia (and Ubisoft's other DRM-free games. I found out that Prince of Persia wasn't the only one. Ubisoft had released a whole bunch not that long ago) got pirated to hell anyway? That's the only reason I can think of as to why Ubisoft would go back on their old DRM-free policy.

The funny thing about all this though is, I bet Ubisoft's uber-DRMed PC Assassin's Creed II is going to end up selling worse than Ubisoft's DRM-free games. Even with Assassin's Creed's popularity. It seems like almost everyone on the internet has declared that they would boycott the PC version or pirate the game. Some have said they'd buy it (but use the crack to play offline). But I'd imagine that those who wish to buy it are in a very small minority.

Indeed. This incident is going to hurt their PR a ton. There will be a huge gamer backlash against the next game to use such draconian methods. Unfortunatly for Ubisoft not many of their games for the PC seem targeted at the casual demographic.

Haha, punishing the right-doers. Awesome.

I was already going to boycott Ubisoft games with this DRM to make a point, now I'm gonna not buy them because it'd be a waste of money too