In case you haven't read this post...
If one were to be going by that awfully-flawed mentality, we would be saying that Mickey, Donald, et al. have been sounding "wrong" since the deaths of their previous voice actors (ie: "Mickey has sounded wrong since Walt stopped voicing him, Donald has sounded wrong since the death of Clarence Nash, etc.).
Leave Steve Whitmire, Eric Jacobson and all the other current puppeteers alone! They're all great, talented and have done the characters justice since they first took over the roles. After all, there's more to a character than a voice--it's about the performance. This whole "wrong-sounding Muppets" thing is just a bunch of baloney that deserves to be ignored at all costs. Those of you bashing the ever-talented (yes, ever-talented) next-generation puppeteers without thinking are completely wrong about them and really need to think before talking!
If you had a choice, which would you choose? A new voice actor that sounds slightly different from the original but is still very talented and knows how to act or a new voice actor that sounds like a 100% dead-on match to the original but has lousy acting skills? I know I would choose the former.