I'd make a post saying exactly that, rather than rely on a thumbs-up. To me, and I accept it's purely a personal comment, a thumbs-up = "This" or "That's funny". Any other nuance, and I'd post...
The logic presumably being that it's better to have a Board where people can give a thumbs up instead of typing "This" in a separate post, but don't have the ability to carry out a vendetta against folk they don't like (by thumbs-downing every post a particular poster makes)? Of course, any...