No, they didn't. They were new additions that caught on as people played with them, just like ROB. I would rather they not bring back half of the veterans we have in favor of new characters, but again, that's me. Not the public. I'm sure most of you would disagree with me about that.
I favor new characters instead of bringing back the old. Certain ones who generally were "out of nowhere" (and weren't really huge parts of Nintendo such as Mario), like ROB, I don't see having a reason to come back besides "some people want him in". The same case will go for Wii Fit Trainer.
I don't even believe "they're veterans" is a good excuse for those who have reserved spots.
We have to think about everyone, not just one group. There are many people who like ROB and probably do want him back; but do we really think the popular idea would go to voting him in when the process of "who actually becomes a part of the cast" is addressed?