We have those vertical-split hot dog buns here in the US too, at least in the NE. They have a special name, which escapes my mind at the moment -- I always have to be careful at the store not to buy the wrong ones by accident. I don't care for them, personally, but I can see how they would work better for yakisoba. (I don't, however, understand why anyone would want to eat noodles out of a bun, but that's a whole other question.)