like most things in the military, yes and no. a lot of things can be true for some, and not for others. what has been said is correct. 90 days is reserve component. active duty deployments depend on the situation-- 9 months is supposed to be the max, with the chance to have them split if everyone is on board with it. there's also a tail end "stabilization" kind of thing where even though you may come back from deployment, you may be stuck with the unit as they re-integrate. so you may be back in the US but you still aren't home.
in regards to specialties-- in general primary care and surgeons deploy more, and funky stuff like path not so much. this has changed though with the brigade surgeon nonsense and even highly specialized people can be potentially tasked for 2 year rotations doing medical admin.
--your friendly neighborhood getting ready for another deployment caveman