If The Muppets on Muppets featured any of Jerry Nelson's characters, then I think we would have known for sure sooner whether it was made for the DVD or not, as Jerry Nelson has retired from performing his Muppet Show characters. I guess Nelson wasn't available for those interviews back when they were produced. It would have been great if Floyd, Robin, and Statler (with Waldorf, of course) were interviewed. I don't know if there were any concerns over character popularity, but those characters would have probably been just as familiar with casual fans as Johnny Fiama, Sal, and Bobo are.
And I guess it makes sense that this was made earlier because of Brian henson performing Sal. Brian Henson hasn't performed for the Muppets much since Disney bought the Muppets (though it seems like he was performing Muppets less in the last few years before the sale). He's been running The Jim Henson Company, and I guess focusing on Puppet Up! and the possible upcomming Tinseltown and Late Night Buffet shows (though Bill Baretta's also been involved with some of those productions). I don't know if Brian Henson has performed Sal since The Muppets Wizar dof Oz (where he only performed the voice). I hope that Brian Henson does perform his characters again soon (and not just Sal, but also Dr. Phil van Neuter and especially Nigel, Seymour, and The Newsman).