Well, I'm far far from an expert in either, but here's my opinion, and it applies to food I've eaten in those countries, not in the US.
Food in Thailand all seemed so fresh and vibrant. I could taste the flavor of every component in a dish, yet the combined flavors were probably more balanced than any other cuisine I've eaten.
In Japan, it was the attention to detail and perfection of every dish. Even a small omelet on a skewer from an outdoor market was delicious. Every piece of yakatori or bowl of ramen, even from a small hole in the wall was good. The fried chicken (not going to attempt to spell it) was as good as anything in the southern US.

Can't really be any more specific than that, it's just that those two food experiences have stayed in my mind, more than anywhere I've been in Europe or the Americas.