The kind of outlet one sees for 240V is to keep you from plugging your 120V iPhone charger into it, not because it's any kind of limitation on the grid. You can have European-style (or Australian, or Vietnamese, or...) outlets in your U. S. house if you like, and pull 220V out of every outlet in your house, you'll just have to do a ton of rewiring. (Theoretically; if I've forgotten something, it's because I've never heard of anyone converting a U. S. house to use non-U. S. appliances.)
Agreed, but there's more to it I think. The primary design goal of the system is don't accidentally start a fire or electrocute yourself. The other effect however is the inverse, a mechanism by which the power company can come up with the right distribution of transformers to get the power to your home. If you have not been wired by an electrician to handle that much electricity, your block may not be sufficiently wired and fused to deliver that much. Because presumably the electrician checks such things before putting buildings on the grid.
Is there such a thing as a 120V-only USB charger?
Well, if we're going to get all pedantic and stuff, I'm pretty sure those old iPhone chargers came with a non-swappable U. S. 120V plug. But for the life of me I can't find one lying within arm's reach at the moment.
What's different about it? All my 230v devices use the same outlet and plug. Or is that on a different voltage and current, power rating alltogether?
If you don't have a 240V circuit handy you can just find two 120V circuits on opposite phases and wire them together