I don't think a "Thanks" post, in and of itself, is necessary. I think, really, it can be assumed. Imagine if the OP responded to every response with "thanks". It'd be too much clutter. A progress report, detailing what actually helped (or didn't), is actually useful for people with a similar question/problem, and even others who provided help.
Yeah, this is pretty crap, and just adds to the noise. You end up having two separate discussions where everyones repeating themselves because they don't see the responses in the other thread.