While Russia would most certainly like to claim that they were preventing a Kosovo-like genocide, simple fact is that Russia is playing old-school power politics; not embracing humanitarianism.
The conflict in South Ossetia (and the one in Abkhazia) has waged back and forth since before the break-up of the Soviet Union, with low-level ethnic cleansing from both sides, although Georgia was the more powerful party. Russian peace-keepers have in fact been stationed in the region since 1992 IIRC.
So why the sudden interest in a two-decades old conflict, with Russian forces already present? Either there was a clear and imminent threat, of a a sudden bout of ethnic cleansing, as Russia would like to claim, or perhaps there were other factors involved.
First, one interesting fact: Russia claimed that Georgia had attacked Russian nationals. The aforementioned peacekeepers? No - Russia had, since some years back, actively been issuing passports to South Ossetians, effectively making most of them Russia citizens! This is, as far as I know, unprecedented, and patently absurd.
Imagine if Mexico issued Mexican citizenship to the Pueblo indians, and then claimed the right to intervene on behalf of these new citizens.
There is also the issue of power - not political but electrical. I don't know if this has been brought up in American media, but Europe is utterly, completely and totally dependent on Russian oil and gas. As much as Europe might want to complain, all the Russians have to do is turn of the tap, and Central Europe is literally back to the Dark Ages.
How does this concern Georgia? Russia would obviously like to keep the status quo and prevent any alternative sources of energy from developing. Azerbaijan happens to be a major producer of oil, and the main pipeline from there to Europe goes through... Georgia. Coincidence?
The Transcaucasian conflicts since 1989 have all been dirty and ethnically driven, not just Abkhazia and South Ossetia, but Adjaria, the Armenian-Azeri wars and several others. It is shameful that the international community have shown so little interest, but it would be naïve to confuse these very proper humanitarian reasons for intervention with cold, calculating realpolitik.
And Russia is all about realpolitik.