They need to have a list of aproved hotels even if it does not benefit them. There are some pretty sketchy places and one would hope, at least part of the reason, is to vet out the sketchy ones. That being said my dad always got a better price through his credit card than the dubs were getting through the borg.
I'd be intrested to know how the prices match up compared to the online sites. I bet it isn't that much different, the hotels have pretty much pefected the art of pricing their rooms. Some of the online sites buy a block of rooms at a discount and them sell them for a profit. I wonder if that is what the borg is doing? That would explain why it is so important to only book using the JW secret code.