The difference between Kosovo and South Ossetia is that before the whole mess started in the early nineties Ossetia had a Georgian majority which was ethnically cleansed, while in Kosovo the Serbs were a small minority. I happen to have a rather restrictive view of the time limits on how much stuff like that matters, but a decade and a half doesn't eliminate them completely even in my view, though it does substantially lessen their importance. To use an unfortunately possible analogy, how many years after an ethnic cleansing of South Lebanon or the West Bank would you view the use of force to reverse the situation as an illegitimate provocation?

Another issue - what makes you think that the West 'pushed' Kosovo to declare independence? More like the other way around.