Both Prof Goldsbury and Clark have valid points...
I think a passenger-facing employee at an international airport would have a greater tolerance for varied English pronunciation as compared to someone deep in the country.. so it depends on one's exposure to people speaking English differently... (either via one's social circle/workplace/TV, etc)
But, yes, Japan is a relatively homogeneous country, and the Japanese appear fond of rules/standards, so people speak hyojungo (standard Japanese) the same in places I've been to.. hence, a slight mispronunciation can be misunderstood... missing or adding an extra sound could mean a different Kanji altogether.. moreover, you don't see too many foreigners speaking Japanese on TV, so there is less exposure (and less tolerance) to different ways of speaking the language ... and... Japanese *has* intonations... compared to English, Japanese appears to have many more homophones, e.g. *hashi* could mean bridge, chopsticks, end, etc.. so you have to say it j-u-s-t right, to avoid blank looks
