Seinfeld is rich. I doubt he cares at all if anyone buys the DVD. Plus, he'd be wise to distance himself from Richards.
I'm not suggesting it. It is pretty much accepted that that was the deal. If Seinfeld didn't care ifanyone bought his DVDs then he would not have timed his appearance on Letterman to coincide with their release.
Actually, Seinfield did arrange that (he was there shushing the audience during the sattelite feed with Richards). I think he did it more to protect the reputation of "the show" and possibly to help out a friend than for money-- surely he rakes in plenty of dough.