"See you later!" is in the same line of conversational mannerisms. Usually used when I don't know when I will see someone (friends, usually) next. If I were to say, "have a good week!" that would imply that I won't see them till the next week. And what then if I see them in between?! When someone tells me, "See you on Sunday", I immediately ponder, "will I actually see them? wait, are they referring to something I planned but forgot? have I double booked myself? uh oh." The only times I'm really comfortable saying the specific next time I will see someone, is when we just finished making the plans to meet up again. If you say, see you tomorrow, and we have not made any plans to hang out, I have a minor panic moment. I know, I'm weird :)
"Have a good one!"
