The reason I don't ALWAYS do it is because I've gotten infractions at many forums for "spaming".
I post: thank you and appreciate the help
A day later find out I got an infraction for a spam post LOL. This is not here, or at least I can't recall it happening here so far at vB.org. But it has come up on other admin forums.
So I decided to not say anything, unless I see lots of others post a thank you.
Better yet, vB should implement the thank you hack.