I guess it depends on the company. Mattel is pretty much the Ernie/Elmo/Cookie group. They do have merchandise that's just starting to feature Oscar, as well as Bert and sometimes Grover.
There was a set of PVC's available at the dollar store (by a company I forget the name of. it's the ___________ Teddy bear company, somewhere in California), and it featured Elmo, Zoe, Big Bird, Cookie, Ernie and Bert. Same thing with Gund. But they also have Oscar and Grover... and they've brought the Snuffy doll from a 35th anniversary product to their current line.
Abby stuff is around, but I don't see much variety with it. I think she will replace Zoe, but to be honest, I don't see Zoe stuff half as much as Ernie, Elmo and Cookie...