I've been watching a bunch of Starcraft II replays recently, and I just realized that I've never seen a single medic in any of the games. The most recent one I watched had medivacs, which is obviously more useful than medics (since they can lift units too), but most of the games I've seen had a bunch of marines and marauders and no healing units at all.
It confuses me because I used medics all the time in campaign mode, to avoid having to buy more marines all the time. Is there any reason why no one seems to do that in multiplayer?