The difference is that there's an "American English" option in the installer. It could be argued that when that option is checked, the version being installed IS specifically/mainly for US citizens, and the only grammar that isn't is:
- Wutai Pagoda
- Gold Saucer Play
- Cait Sith
In all of these cases, there is a story reason for them to use a different dialect than seen in the rest of the game. Even using international English spelling and grammar, all three of these cases would end up being different from the rest of the game. They're
supposed to stand out. Cloud, on the other hand, should be expected to use the same dialect in this sentence that he and every other "non-descript dialect" character in the game uses, which depends on whether or not you check "American English" in the installer. It's certainly not the same as removing Cait Sith's accent.
That said, I did some looking into this, and "give it us" is even regional within England, some areas using it and some not.