Morkus from Orkus
Sorcerers have no ability to cast every single spell with no somatic or verbal components. They can get very close if they use up every single one of their sorcery points on doing so. That's two differences right there. They can't do them all, where a psion could. And there's a cost to doing so, where there would be no cost for a psion. Those two things are meaningful differences.You need a hand empty or a feat. Other than that, it's the same thing. I wouldn't call that a meaningfully different mechanic, particularly since a sorcerer already has a specific ability to do just that.