At the end of WWII it was not the Communists who beat the Nazis but the Russians who beat the Germans. It was the armies of mother Russia who stood on the line dividing east from west, who'd lost 25 million dead to get there. They weren't going to give an inch to anyone...and certainly not to Westerners who they suspected - with good reason - stood by while they suffered and jumped in at the end and grabbed as much as they could.
Sure, Roosevelt could have refused to confirm legitimacy, refused to recognize their conquests. A lot of good that would have done.
I don't see any posters observing just what Bush was doing by bringing this up before he went to Russia.
He was thoroughly rubbing Putin's nose in the evils of communism to force him to prove just how serious Russia was taking democracy. Sort of a "are you serious, or not?" type of stance.
It certainly didn't hurt to bring up the issue while in the presence of the countries that were brutalized the most by the horrors of communism.