I don't really see American Smooth as being more "limited" than International Standard. I think that, at least for competitive purposes, it requires a lot MORE knowledge: arm movements, use of the head, leading/following without always being in full closed body contact (open work), etc. As Jonathan pointed out, for exams and competitions the technique is the same for smooth and standard with regard to use of feet, ankles, the closed hold, etc.; and alignments and degree of turns are pretty much indistinguishable.
I learned American style first, and didn't really find that I had any major adjustments to make in following International patterns - all you have to think about is closed body contact. But I have heard some women say that they learned International style first, and had a hard time adjusting to American style because the lead/follow in some smooth patterns requires a different kind of sensitity than only closed body contact.
And, at least in competitions in the US, a lot of Standard dancers seem to use quite a bit of American-style open work when they dance their solos.
I do like both styles of dance, but I prefer American because of the great variety it allows.