Presuming that the IPO suceeds, Hilton will now answer to Wall Street. Even though points have $0 value to the consumer, they are a liability on Hilton's books. From time-to-time investors will nudge Hilton to get various liabilities off the books. One way to do that is to simply increase the # of points required for a given service, e.g. a night.

Points will follow cash prices over time. If the cost of a given room increases 10% over time (not talking about one-off issues), you can expect it to cost 10% more points over time.