You could specialize cities with Simcity 4 region play also. The point is that it gave you an option to do that, rather than forcing you to do.
Anytime someone says "game intends you to" it's probably an example of terrible game design.
It's not like they purposely ignored that possibility. It was just not possible with respect to allowing most people's PC to run GlassBox/the game with it, which is why it'll come as DLC. I rather have the game now, working for most people, with regional play and bigger cities than DLC, than having to wait another year or 2 until either the engine has been perfected and/or consumer hardware has cought up.
I played beta 1 and I found that it restricted you to specializing your cities. The game encourages this behavior with having a "gambling" or "coal" city. It's pretty much impossible to have a city that is focused on multiple things in this game.
And that's good this way. See paham's response below me.