Julia, some of the hardbacks you've seen may be book club versions, which are most definitely cheaper. Though I recently received three original-publisher's versions from the Mystery Guild; I can't imagine why or how this works out since it was billed at $11.99 as it would have been for their own versions.
I've tended to believe that as long as I had all the words, properly formatted, that I'd be happy regardless of whether it was a book club or regular hardback version, but lately I'm taking more pleasure in the better quality books. (This could have to do with the disposable income going up in recent years too!) My books run the gamut from new high-quality hardbacks to used paperbacks, but since I only buy books that I want to keep, I hardly ever get rid of any unless I replace them with a new copy.
Barbara, is there any chance of doing POD with any of the others?