The problem with spend-based schemes is that the way flights ticketed by alliance partners credit becomes very convoluted since, for instance, United doesn't ha

The problem with spend-based schemes is that the way flights ticketed by alliance partners credit becomes very convoluted since, for instance, United doesn't have any idea what you paid Air Canada to fly from Bangkok to Hong Kong on Thai Airways. So we end up in a situation where United's mileage credit rules could actually encourage you to fly, say, ANA from SF to Tokyo rather than United, which is exactly the opposite of what they were trying to do a few years ago by harmonizing mileage credit rates for their trans-Pacific joint venture partners. Status wasn't just supposed to encourage you to spend more with your home airway, but also to prefer their alliance partners when you travel outside of your airline's route network and I think that concept is rapidly being weakened by these spend-based schemes.