What could be the reason for accepting an answer but not upvoting it? Situations:

1. Accepting own answer - ok, no upvote on self-answers
2. OP not having 15 reputation cannot upvote. I think that OP shold be able to upvote answers on his/her questions even if he/she does not have 15 points yet.
3. Uninformed or rude, does not care, got his/her answer, checks and leaves.
4. Got some answer, but does not see it as good enough? What? ...should not accept.

I simply cannot think of valid scenairo (except self-answer) when you (OP) would accept but not upvote an answer. Should't the upvote be automatic on accept? (I mean automated by SE - feature request.)

EDIT: To make myself clear, I would like to propose, that accepted answers be upvoted automaticaly, except for self answers. This automatic upvote should not count towards daily limit (max 40). My reasoning is, that accepted answer is helpful and should not be accepted otherwise.