It's the package that's the bargain, the combination of flight and hotel is often very attractive and having an extended payment period is also helpful. From what I've seen in this area, when BA does a deal with hotels for a low rate for its bookings, that low rate seems to stick even when the hotel is filling up, So for some hotels they see the overall benefit of the arrangement with BA over and above their policies to charge the maximum possible. Corporate rates in this situation tend to drift upwards (they are often fixed percentage discounts) but BA's rate won't. So it does pay to shop around, particularly if standalone hotel prices seem a bit high.