there are some "plus" and "American" sizes in the Italian seats. sparco's EVO seat comes in 3 sizes now for this reason, and most companies have a t least one winged and one non winged seat made in skinny and American nominal sizes.

but yeah, country of origin dictates to some degree the size of the seat. stay away from tubular steel FIA seats, too. the pressure points on the shoulder for wider guys are really bad with those in my experience (I have wide shoulders myself)