I answered a question, and the user who asked it, accepted it.

That user didn't give me an up-vote.

Is there ever a good reason for not to up-vote the answer (except for not having sufficient privileges)?

(examples of the types of questions in question are :[this one](https://superuser.com/questions/350388/how-to-migrate-a-microsoft-virtual-pc-vm-to-a-physical-disk/350534#350534) and [this one](https://superuser.com/questions/347891/is-it-safe-to-uninstall-asus-eee-dock/347910#347910).