First of all it's courtesy, secondly a reply/ acknowledgment will often draw out more on the subject as someone like you would have scurried off to find something, and come across more and be so close to post it for us all that a small thanks might trigger that. I'll often answer something briefly just to get it done and be sitting on more.
At the end of the day it's the people who ask and don't thank who miss out.
Like the others said your stuff is gold, and appreciated thanks.