I am sure that no-one under-estimates the US contribution to the Allied cause. However as to speaking German. Before the US rode in with the cavalry, Britain and her allies had stopped the German invasion of England, sunk the Bismark and captured a U boat with its enigma machine. Now that might mean that many other countries might be speaking German but not necessarily the Poms.You can complain about having to pay back a loan, but face the truth, if the US hadn't loaned the UK money and arms, you'd be speaking German right now. About 419 thousand American's died in WW2....only slightly less that the UK's 450k. While others lost more, our own "contribution" on that front was not minor. (link) So, yes you got the **** bombed out of you and we didn't. That's a result of strategic location, not design. If the US had been within range, it would have seen more enemy damage than it did. Contrary to popular belief, the US and Canada -were- attacked directly on several occasions however damage was minimal due to the logistics. Had England fallen, or had Midway or Hawaii been taken, more damaging attacks would most likely have occurred.
It's a bit like saying "If it wasn't for the American's we would all be speaking Japanese in Australia." In actual fact the supply lines to Australia were probably too long and exposed. And it was the Australians who, against the odds, stopped the Japanese in PNG on the Kokoda track.
All the allied forces suffered mightily in the war. The figures are available on the following site.
http://en.wikipedia.org/wiki/World_War_II_casualties
More than straight casualties, look to the percentage of population of the casualties. UK 0.94%, Australia 0.57%, Canada 0.4%, US 0.32%.
Let's not be too precious as to who did what. The important thing is that eventually the world got its act together and we have benefited ever since. Now many of our countries are embroiled in Afghanistan and most people would wish we weren't. History will judge whether the deployment there was right or wrong. The important thing is that despite providing the overwhelming numbers of troops etc, the US is not alone. Australia, UK and other Nato countries are in the s#*t with them. Although this is not particularly up to date it does give an indication of who is doing what. Note that after the US the UK has a large contingent followed by Germany and surprise, surprise ... France. (The US figure is corrected in the body of the article)
http://www.guardian.co.uk/news/datablog/2009/sep/21/afghanistan-troop-numbers-nato-data#data