Sad Emo,
I wouldn't have expected such a high figure for Britain either (I would have "guesstimated" the UK more like 1/3 way from continental Europe and 2/3 from America, just a bit farther West than geography would require, as ever ).
What strikes me (not only from those figures, but from my own European perception) is the relative cultural unity of Northern continental Europe in spite of huge historical differences: Scandinavian atheism is born on Lutheran ground, Dutch on Calvinism, French on Catholicism. The religion wars were strong in France but not everywhere else, and even here atheism developed much later. The relationship between Church and state is the opposite across the French-German border, yet the proportion is similar. The communistic experience in former Czechoslovakia and Western USSR doesn't seem to have made a big religious difference either (with the notable exception of Catholic Poland).
I wonder, btw, if the USA are not more religious (in the fundamentalistic way) now than 100 years ago, so maybe looking for causes in long-past history (or the lack thereof) isn't sufficient. -- Btw, I do not intend any USA-bashing here as done4good puts it: those are really interesting and complex questions.