All the big brands get around this by offering cheaper pricing restricted to their rewards members reserving directly via the brands' website or call center, which is non commissionable. It's free to be a rewards member for all of the hotel rewards programs, so there's no reason not to go that way if your goal is to spend the least amount of money.
Edit: I'm going to have to retract my comments about cheapest price being on official hotel brand websites. I did a cursory search and find many cheaper options on Hotel Tonight (and expedia) for same day reservations than the brands, and while I haven't looked at all the brand's best price guarantees, at least IHG's exempts them from having to provide the lowest price within 24 hours of checkin, so it seems like a loophole to let them dump rooms for cheaper on third party websites day of arrival.
