As long the comment is not spam or some other type of crap; that should be enough for the author to give any comment under their own post a vote!
Especially if you think not enough posts are getting the reward they deserve ... if you were to reward your followers that comment on your posts; that would actually help! just saying ...
For some people, who actually get hundreds of comments, just to keep up with it, would be too much. And of course only comments that start a new tread, not comments in reply to other comments, that would be too much as well. And sure, only the first 48 hours or so. And of course only proper comments, not silly little lines like; I like your post, or some excuse to drop a link to their own post and the likes ... obviously!!
But when I see a post with not even 20-30 comments, and although the author usually replies and upvotes some comments, when they don't upvote a lot of the comment, it just seems like such a lack of etiquette.
To me it seems that giving acknowledgement to those few people that actually liked your post enough to not only open it and read it, but also comment ... it's just a matter of good manners that you show your appreciation and upvote their comment.
Think of your post as an invitation towards the world to come and visit you and have a conversation, upvoting is like taking the time to make sure you welcome and shake hands with everybody who comes to your party with the best intentions. Sure, kick the drunken dude out, but make sure to walk over that shy person from work that came over, but has nobody to talk to ... you're the host of the party; make sure everybody has a good time ~ don't be like the whales!
And people appreciate it, you will get more followers from doing it. So, make sure to upvote enough comments on your own posts.
Happy Steeming :)
(don't forget to upvote my post! thanks)