I don't think Seinfeld would really stoop as low as to just appear on any old show in order to promote something, it would be a show he likes. I have huge respect for Jerry Seinfeld, he made a clear choice to end Seinfeld when he did even though NBC were offering ridiculous amounts of money for him to continue and then he decided he wanted to go back to stand-up and didn't want to be one of those actors/comedians who try to hog the limelight forever.
Oh and also yes Tina Fey is hot but they try to present her character as not being hot..although she quite clearly is.