I'm not sure Uncle Sam would have won the war either( Britain would defiantly not have won alone.), had Hitler not invaded Russia, than a stalemate would have ensued, Rommel may well have won in the desert if he had all the Eastern Front troops at his disposal.
The general opinion (by historians at least) is that it took all of the big three to win the war. Each individually (Well, except Britain) had the resources, man power, and industry to be able to defeat Nazi Germany, only none/neither of them were in the right strategic position to do it, so they required the aid of one another. America was on the other side of the Atlantic and the Soviet Union made some crucial mistakes at Barbarossa's start, mostly due to the unique politicization of their army, that almost cost them the war, and negated them of some of their greatest benefits.
Even if there was no Eastern front, Rommel would not have any more troops coming his way; His logistics were pretty much already stretched to their max as things were. Unless they managed to somehow end Britain's naval dominance in the Mediterranean. Even if he could pull off a victory, it gained nothing for Germany, really. The goal was simply to cut British supplies from their colonies. Certainly a huge nightmare for the Brits, but Germany would be no better off.
Stalingrad is what broke them so yes I am grateful to the Russian war contribution. They could just have easily signed a truce with the Germans like Lenin did with the Treaty of Brest-Litvorsk in 1917 and given away a chunk of their territory
Stalingrad wasn't actually that much of a loss for Germany, rather it was more of a moral boost for their enemies. Even after Stalingrad Germany was able, and indeed still carrying out massive offensives. It was Kursk that lost the war for Germany, as they would be forced on the defensive, and we all know what that means on the steppes.
Germany would never have signed a treaty, remember they were there for Lebensraum. It was life or death for both sides.
To the topic itself, my opinion is that those Poles who actually know their history or care about it, would tend to be ungrateful. Only a few wouldn't. Its stupid to blame the Russians however, (First of the Soviet Union was hardly composed solely of Russians) as Stalin was its complete ruler. He was obeyed or people died.
I do not think Poles should be grateful, really, but being Anti-Russian because of it is simply stupid. Of course Poles would rather not be dead, but having their freedom taken away again afterwards is barely a substitute.