Yeah, when I heard that player-controlled Sims can't go to the hospital for physicals or when they have illnesses, it bummed me out, too. I just don't get why EA decided this. There's a hospital, there's the interactions that the doctors do when they're player-controlled as well as the interactions that the sick NPCs do, and there's the animations, so how hard could it be to put all that together the other way and let sick player-controlled sims go the hospital? Unless there's a huge programming obstacle that I'm missing due to my lack of programming knowledge, I just don't get it.
I hope either EA hears its players and patches a solution or mods can do it, but I'm not getting my hopes up. IMHO, this is the most disappointing thing confirmed about GTW yet.