I always thought that my heroes could use their command abilities every turn. Is this the case? Or have I just been misreading the rules all along?
Just the general can use em. With some exceptions like the Starbeast constallation. Also, if a general knows more than 1 he can only use 1 of em per turn. Frankly it's a bit odd given that for a lot of heroes the command ability is what makes them stand out as a leader-type unit, it's weird to field "leaders" if they do nothing that resembles leading...
What @Canas said. But there are a few exceptions. A notable one is the Bloodclaw Starhost which allows a few other heroes to use their Command abilities as well.