What an interesting discussion. I have been thinking about this a bit lately too. It's fascinating to read some other perspectives on this here, and hear about other people's experiences of roleplaying outside the US.
I'm Scottish, but I've lived in Japan for coming on six years. My wife is Japanese, and I am considering introducing her to roleplaying. This brings up all sorts of interesting cultural differences, as I have to struggle from the very start with explaining the very European/Western archetypes used in D&D classes. Moreover, Japanese literature is quite far removed from Western literature; the Japanese translation of the Lord of the Rings is considered a very difficult read here, and very few people seem to have read it. And of course reading in general tends to be overshadowed by manga. So it's hard to know which parts of the picture she is familiar with at all.
Regarding the sweet potato ice cream, I haven't come across that one, but I have tried soy sauce ice cream (lovely!), soba noodle ice cream (hmmm), spinach ice cream (yuck!), rice ice cream (not much of a flavour, interesting texture), sesame seed ice cream (another hmmm), and probably others I've forgotten about. But I have to say, I don't think you should take any of these strange and bizarre flavours as an indication of how different Japanese culture is; most Japanese people find the idea of these flavours just as strange as you and I. And there are strange cooks in all countries - consider the recipe for beef roasted in Coke I once read in my local newspaper back home.
Nevertheless, the issue of cultural backgrounds is absolutely a real one, which for better and for worse I have to live with every day.