I have yet to watch the clip of this recent incarnation of Kermit (plan on doing so tomorrow when I'm home). But I can think back to when I heard Steve perform Kermit for the first time on the Muppets Celebrate Jim Henson and remember having alot of mixed emotions. Heck, I never even went to see Muppet Christmas Carol in the theater because I wasn't ready to see the "new" Kermit in a full length movie yet.
But obviously we all warmed up to his portrayal of Kermit. Whoever it was that performed Kermit on this show, had like Steve did at one time, big shoes to fill. I am sure there is a logical reason that Steve couldn't or didn't perform Kermit for this appearance. Do we know if they're still filming that stuff in Disney? Maybe his schedule just couldn't comply. Maybe he has personal family stuff going on and had to fly back home to be with them.
I understand people being upset that the Kermit we're used to wasn't there but let's give whoever it was a break. If he was a last minute replacement, that's a lot of pressure. If there was another reason behind them having someone else take over for one night, I think we should still adjust. Like many people have said on the fan sites, the general population won't notice the difference and will still embrace Kermit. And I'd rather see a "new" Kermit than no Kermit at all anymore.