The conflict in Georgia whilst not the same as actions taken by the Allies in Iraq, Afghanistan or Kosovo, set certain precidents. The Iraq action in particular.
Simply put the action taken by the U.S.A. and the U.K. seriously undermined international law and authority whilst also weakening the image of the U.S.A.
Further to that the USA is engaged in two active conflict zones.
No longer does the USA seem to be the protector of Freedom, instead it seems to be the monstrous oil thief, parading its way around the world enforcing its ideals on others.
So, why shouldn't Russia? (That being the reasoning behind the Russian government and people I suspect.) The USA and UK invaded sovereign nations that were substantially weaker then themselves. There were varying reasons behind these actions, oil, terrorism, past annoyance, securing jumping off points for future actions.
It's a curious situation, will Russia annex Georgia, or withdraw after it has plundered it. I'd strongly suspect the second option, it unlike the USA and its allies in Iraq and Afghanistan has little need to stay there.
The reasons to completly destroy and intimidate Georgia is to show those around it that it isn't a joke, and that it is willing to launch brutal decisive attacks when it deems them necessary.
The Georgians misjudged this situation, and gave Russia "casus belli" against them, the Georgians expected that the Russians wouldn't be quite so prepared and quite so aggressive. They probably expected (at worse) that after the Russians had regained South Assetia (without launching many attacks outside of the conflict zone.) The west would give them more aid and support, possibly fast tracking Nato membership.
Of course that was overly hopeful. There is one thing that we can all be certain of Europe/Russia/China/USA never intend on having their troops in direct conflict.
But if it happens, my, we will be living in interesting days indeed.
I'd say that the "Western" actions are more like colonialsism (but not quite) or old fashioned cold war stuff. Whilst Russian actions are more Expansionism.
Of course there is a difference between the USA and Russia, the USA is mostly surrounded by water, with a friendly nation to the North. Whilst Russia has a large number of borders.
Also from Russian eyes nato and EU encroachment east is seen as expansion into their "backyard."
So it's curious, did the Russians trick them in the first place or Had they anticipated the Georgians assault? If it's the second option, why didn't they already have the forces in South Assetia to repel them? curious.