Manufacturing, storing, shipping and supporting two different models of basically the same phone is probably more expensive than just deploying the one model with the removable battery everywhere.
To elaborate a bit: This is very different than providing models with different radios/modems for different markets. A different radio/modem probably only requires a single, different component(?). A model with a replacable battery requires a different battery design, a different case design, different seals (to make it waterproof) and most likely a different PCB layout, too. That is a tremendous amount of effort compared to swapping out a component or two on an otherwise identical phone.
That's why I think it's not unlikely that replacable batteries might become much more common globally once this law is being implemented and applied.
Both US and EU are big enough markets that two models are totally feasible. Actually, radios inside cell phones are already different due to slightly different frequencies between the two continents. Take a look, but a lot of phones have US and EU version already.
While that is true, having 2+ radios for various global markets is much less of a hassle than having to design and manufacture at least two different cases, seals and possibly PCB layouts.