You are not entirely right here, but not entirely wrong either. While just doing that doesn't favor any particular strategy for specialization, it could be argued that building everything IS it's own strategy. As I've mentioned, while I do like have some of my cities be specialized, other cities just build everything and thus are 'general purpose' cities. While they can't ever do anything specific extraordinarily well, they can do everything to a lesser degree. There is nothing wrong with this approach, even though you seem to be implying that there is. If you don't favor this particular play-style, that's fine, just don't try to say that it is invalid.