PlayStation users can't change their PlayStation Network names because PSN wants to curb the behavior of griefers and other online malefactors, or at least not give them a tool to use, the president of Sony Computer Entertainment America tells IGN.
Shawn Layden, responding to a long-running user request put forth by IGN's Colin Moriarity, said that "the road map for feature extension is long," and that changing a PSN account name is on it. "We want to give you more control across your experience," he told IGN.
So why not?
"We don't want to make it so that you can go in, grief a bunch of people in Far Cry, change your avatar, change your username, go into CoD and grief everybody over there. We want to stop that."
Gamertags are, of course, changeable in Xbox Live — for a fee. That fee probably cuts down on the rampant switching scenario that Layden describes above. He didn't say whether PlayStation Network would make name-switching free or a paid service.
There's more detail in IGN's story, but the gist is that bad apples, or the threat of them, are what's holding back this implementation.