I agree. A comment of 'Thank you' is not the way, but I did say:

If you really like a post, say so. Say exactly what you did like - and if you're polite and respectful and can give constructive criticism in a NICE way, do that too. I for one, will appreciate that and thank you for it.

And this:

When you vote on something, you say, 'Thanks for the work, thanks for entertaining me.'

The upvote is for saying 'Thank you' - the comment is to say a little something more... like you just did :)