And where would you do overhead presses? Behind your neck? Permanent shoulder damage. Through your skull? Impossible, of course. Any overhead press must start in front of one's head, and gradually move to the middle of it as it goes up, which makes all overhead presses mainly a front deltoid exercises (despite the fact that they do engage all parts of the shoulder), no nothing wrong there.
The anterior part of the delts is done with any press imaginable, be it vertical or horizontal. As for isolation exercises, front raises, front presses, push-outs are all great for front delt stimulation. Just remember to compensate that work with exercises done for the rest of the shoulder muscle.

posterior deltoid exercises? reverse flies/flys (how the heck do you spell it?)
chin-ups, all rows...

posterior deltoids are used when you pull your arms back.
anterior deltoids take action in all pushing exercises (hence why people say often you barely need to train them)
lateral deltoids do something when pulling the arms up, pretty much.

correct me if i'm wrong, of course. that's what i gathered so far.

good information to know