I think I do have to add one more thing, in order to be fair. Steve has a handicap that Jim never had to contend with--Steve has a boss. Jim WAS the boss, and--by default--Kermit got to be the boss, so whatever Kermit said was, well, the way it was. Steve never had that luxury, and it HAS to matter.
The way I see the progression is this: (and this is mostly my audience eye-view, which was informed by various personal appearances) When Jim was doing Kermit, and Frank began to do Piggy, Jim and Frank had a marvelous chemistry for characters of all sorts. Bert and Ernie, Kermit and Fozzie, Kermit and Piggy. They were not in the least afraid to do something crazy, something taboo, something naughty, something different, because the truth of the relationship between the characters always undergirded what happened on the, um, stage. The affection and respect with which they treated their characters and each other always came shining through.
With Jim's passing, the mantle of Kermit passed to Steve, although when it did, it did so minus the understood leadership that went with Jim being Kermit. Initially, I thought Steve's Kermit was very sweet to Piggy, in MCC and MTI. Kermit shows Piggy deference and tenderness, and often bows to her whims when I thought he actually might have stood up to her, or at least tweaked her a little when it was Jim. Under the circumstances, this seemed very normal, and I thought it nice of Kermit to let Piggy get used to the, er, "new him." You can also see some of this gentleness in the Muppet Fairy Tales, when Kermit is always portrayed as nice to Piggy. I know that Frank didn't do the puppetry--just the voices--for that one, but the relationship dynamic is still valid. Also about that time, Kermit Unpigged came on, and Kermit is--again--exceptionally deferential to Piggy. Later on, when Eric took over the role of Piggy--an ENORMOUS mantle (and if anyone makes a crack here I will HURT you, and THEN sic the penguins on you!), Steve had settled into Kermit, and it makes sense that the more experience character would take the lead in character interactions. Somewhere about this time, Kermit apparently decided that the former love of his life was more annoying than adorable and that having a serious relationship (forget the fact that they were actually married--everyone else seems to have forgotten) was apparently cramping his style as some sort of hip "playa." His interactions with her--both on the screen and in behind-the-scenes shots--became colored with insults and snarky comments. Let me say for the record that Jim's Kermit could be remarkably grouchy and sarcastic--sometimes he was downright mean to those who ran to him for reassurance, like Fozzie and Piggy--but at the end of the day, you knew that Kermit would eventually work it out with himself and come back, sheepish if not apologetic, and make things okay. (A good example of this is the Bob Hope appearance when Piggy tries to "give" herself to Bob Hope. Kermit goes along with it, even teasing Bob about "sweetening the deal" with $5 so Bob will take her. By the end of the show, Bob, Kermit and Piggy all know that Piggy and Kermit belong together.) But THAT resolution stopped happening.
We got sarcasm or, well, maybe just immature jokes, lots of evidence that Kermit enjoyed those moments of cruelty and then...not much in reaction. For a while, it was as though Piggy didn't realize she was being dissed by the person--er, frog--that mattered more to her than any other, um, being on the planet. Those times did make me cringe because it put Piggy in the unhappy position of being the "faithful girlfriend" of someone who cheated on her and made crass comments behind her back. And it suddenly became--yuck--normal to imply that yes there was, um, that aspect of their relationship but nothing else. At this point, if Kermit was a regular guy, he'd have worked his way right off my Christmas card list. A guy who, um, enjoys the company of a girl, who takes her places as his date but then derides, insults and makes fun of behind her back--yeah, a real prince of a guy, if you catch my drift.
And can you imagine Piggy's hurt--and her NON-reaction to something like this? The Piggy I knew from TMS would have taken Kermit's head off. or simply found one of her many admirers to take her off his hands--perhaps both.
In the midst of ALL the WILD excitement over the new movie, where everyone who has any inside information is just GUSHING with praise (for which I am very, VERY glad), the response is rather quiet when asked if the old romance we had come to take for granted in TMS and the subsequent movies (THINK! REMEMBER what a BIG ROLE the romance played in the first three movies!) will be present in the new movie.
I think my best (un-spoilered) guestimate is that young fans--fans who don't remember the romance--will think The Muppets are back just like they always were. They will think this because the "not-a-Piggy-fan" Kermit is the only one they have ever known. And in the midst of all that celebrating of the return of the muppets (which I WILL be doing), I will still not forget what they were like when they were young--and I was, too.
This is my last epic post on this subject today and in this thread. I have no wish to shanghai the thread to talk about something that most fans don't seem to care about, but I'm not going to give up hoping that I'm not alone.