Another reason to explain Russia’s halt: this isn’t your father’s Soviet Union. Russia is a nation in demographic freefall and has little tolerance for taking casualties.
The last few days we’ve heard something like ten Russian “peacekeepers” killed in the Georgian assault on Tskhanvali, then 3 or 4 Russian soldiers killed each day. If their casualties were actually much higher, then the war fever of the Russian people will quickly evaporate.
Don’t forget, it was the Russian Mothers that got them out of Afghanistan and the first Chechen war.
The number of Russian casualties is very likely one of the most critical metrics of this conflict.