So am I right in thinking that you're saying if 2000 people died, the invasion was justified, but if 133 died it wasn't? By that reasoning, how many people would have needed to die in the attack on the World Trade Centres before the invasion of Afghanistan was/wasn't justified? If only 200 had been killed would the US have shrugged it's shoulders and decided not to invade? More interestingly, think about it in terms of the % of that countries civilians killed - if the rough estimates available are accurate and about 70k people were living in South Osseta, and 133 of these were killed, then thats ~0.2% of the population. The % of the US population that died in the attack on the world trade centres was ~0.001% (so 200 times more people proportionately died in South Osseta to use your own (likely underestated) figure). Or to put it yet another way, do you think that Britain (as a main ally of the US) would be justified in going to war with a country if that country attacked the US and killed 600,000 people? A poor comparison (since it'd probably be more likely to be the other way around, and the case of South Osseta isn't quite that simple anyway), but it hopefully helps illustrate the point.
End of maudlin27's quote
Indeed, the US had 241 Americans killed by a Hezbollah bombing in 1983, and we didn't send in our whole army in response. You're argument doesn't work, because there is no calculus for calculating degrees of morality. Americans are far more angry about the 4000 people killed in the World Trade Center than they are about the 6000 that have died fighting in Iraq.
http://middleeast.about.com/od/terrorism/a/me080214.htm
If the Georgians had indeed begun ethinc cleansing, it would be justified for Russia to enter South Osssetia and stop the slaughter, but go no further. There was no genocide, and the Russians even continued to invade beyond South Ossetia. Thus, they have no justification for the invasion of the Georgia.
Furthermore, the people in South Ossesita are not Russian, no more than the Georgians are Russians. Rather, Russia has consistantly attacked (and annexed) Georgia since the 1800s, and this attack is no different.