As a DM, I've been altering alignments to suit my plot goals since way back in the B/X days. During an exploration of the Caves of Chaos, the party rescued a Lawful orc henchman that had been tossed in prison by his chieftan to rot. That orc lasted all the way to the Isle of Dread (the old Expert set module) and IIRC he got eaten by a T-Rex while covering the party magic-user's escape.
So yeah, this is an old tradition. It's cool to see the 4e designers explicitly incorporating it, though, much like Keith Baker did for Eberron.