When you want to vote for a comment, it says: "This comment adds something useful to the post".
But there are many examples that a comment has received many up-votes just for being funny; so the comment doesn't add any useful thing to the post in these case(s).
For example, look at the most up-voted comment on this post.
Why not for example "I like this comment" if we can up-vote funny comments just because of their funniness? Also, this title can serve for useful comments too.
First of all, while not particularly off-topic on this per-site meta, such discussions about the broader workings of the SE framework usually fare better on the main meta site.
That being said, I think you're actually doing it the wrong way around here. What you're proposing would be adapting the tooltip to how the feature is used, however possibly wrongly, rather than using the feature in the way you're told. And in fact you're simply not supposed to upvote comments because you like them but because they're useful.
And in fact, comments that are funny but don't add anything useful to the post aren't really good comments and being funny isn't really a good reason to upvote them. They might also disappear any second for any and all reasons imaginable, such is the nature of comments, especially, well, useless ones.
Now of course we're all humans who find things funny and who upvote things that we just like. Neither will anyone die from a few comment votes on a comment that technically doesn't deserve them. But still this doesn't mean we should advertize wrong usage. What we can do and what we should do are different things and I'd prefer guidance of this kind to strive for the latter.
