There is a very fine line between voting for no reason and spam up-voting. Technically, the person you upvote doesn't have to be the same person. If you're giving away tons of free points then it's still spam. Asking for votes is outright rule breaking. Not a major issues obvi, but it gets annoying.
On the bases of "giving upvotes cos they wanted too", this does actually lead to the same thing with downvotes. As long as you don't get spammed with them constantly, people would lose points over it. Again, not a massive issue, but it goes through the same gateway, so to speak.
One more thing, users with points to spare are free to give the odd downvote to this type of thing. as long as you don't get mistaken for spam downvotes, correcting votes as it were is fine. It's only 2 points for you and you get them back eventually anyway xD