Heh.Re: lack of Muppets...from a directorial standpoint if you include too many characters in there, it's not as easy to immediately spot the gag you're "supposed" to be seeing. From an explanation standpoint, no doubt we were seeing either (a) the first Muppets to take their seats in the theatre (with everyone else still at the concession stand or trying to find a parking spot) and/or (b) it was a matinee.
Seems like the problem was performer availability... more Muppets means more puppeteers. And we'd either see empty seats or Muppets sitting perfectly still and looking...well.. dead. I don't want to sort through and sift through all the Ernie and Bert at the movies segments... but one of them had some Muppets in the background just sitting there.
Somehow a Muppet Movie ending sized crowd would have made this thing look even better, though... but there definitely wasn't a scad of Muppeteers or extras to perform some silently. Though, the point still gets across.