Well, first of all, I'm certainly not advocating that "if everybody just plays in tune then everythings fine" except in the sense of any instrument that can be tuned should be if possible. If you have to use studio trickery, fine. Sometimes its the only way to get the job done.
Second, Varispeed...like so many have said...alters both pitch AND time. This is really NOT what's needed to simply get an instrument to sound "in tune" with the mix...unless you want it to sound different to it's original sound as well. Which, for some folks, I cannot imagine what they really want or need. Go on with your bad selves.
Third, as I noted, there were instruments on Mike's list that can be easily, or with some professionalism, tuned (twelve string guitar, etc...) and should be. BUT...
Fourth, to agree with what bvideo said, these problem instruments do not always go out of tune linearly and "varispeed" as you would have it or even simple pitch transposition without time alteration would not solve that problem at all. The instrument would still be out of tune with itself.
Fifth, many instruments which arent in tune and/or cannot be tuned are simply recorded as is (i.e. my steel drum reference) and we've grown accustomed to their "out of tuneness".
Sixth, I heartily support the addition of ANY new feature that will help folks do whatever in the heck they think they need to do with it. But I also think it's important to use correct terminology when describing said feature and to have valid reasoning to bolster their argument.
Seventh, with the new abilities in digital technology there are many different ways of skinning the "out of tune" cat (although we tend to frown on out of tune cats in our jazz sessions) that are available right now both within and without Sonar.
I hope this is "clear" enough ( I really was asking a sincere question there, ol pal). But if it's not, that's OK. But I grow weary of this now and need a good nap:-)