Yes I think it would also be useful when people ask if I am willing to send - I hit YES and then nothing...
So this has happened with a lot of books that are on people's Wishlists. I can understand that people might not want to give me 6 points for a book they hope they can get for 1.
But the book gets reserved, and no one else can mooch it for a few weeks. If people want to offer me a book from their country for one of mine then the points even up. It seems there are a lot of Americans (maybe others too?) that are not willing to Mooch 2 books to make up for the postage costs.
I think this can be the only reason why people ask if I will send and then don't mooch it. BUT its quite annoying that they do not write and say they changed their mind or whatever their excuse is for not going ahead after asking.