[microcolonel]

I think that if Americans try, it's a lot easier to go to the Japanese phonemes; given that they are effectively a subset of English phonemes (with some variation). That said, it seems that Americans feel like they're making a disrespectful accent when they're getting closer to pronouncing things correctly. They would rather be authentically bad than sound like they're making fun of an accent. Here in Canada we have this problem even when kids are learning Québecois French in school; they think they sound like they're making fun of Francophones when they get close to good pronunciation.

An American English speaker can generally approximate る and similar sounds far more easily than a Japanese speaker will learn to pronounce l or figure out the th in the. That's assuming that the English word they're trying to say doesn't have consonant clusters, which (aside from nasal consonant pairs) simply do not exist in Japanese. It really is not equivalent.