Well I can't speak for anyone else of course but generally the only time I C&C a photo is if it's a wildlife pic, since those are the kinds of pictures I take that is what I feel comfortable with offering advice on. As for my own experience with C&C, I've posted a couple and never gotten a response - but so be it. Sometimes I imagine it's a probably a timing issue, if a post doesn't get a response and a lot of other stuff gets posted it gets pushed off pretty quick. I've never taken it personally.
Yeah, that happens. But sometimes you can see the thread has had a lot of views, but no responses! Not everyone needs to respond, obviously, but when you see 35 views, 0 comments...you're like, "huh?" And plus, if it's something out of your niche, it can sometimes be even better for the OP since someone isn't focused on the particular skill in that area, but the overall big picture.