Originally Posted by mecabq
Also known as semi-dishonest marketing for less savvy fliers. Perhaps they're also to cheat one out of miles/segments. For example, I used to take NW DCA-MSP-ABQ frequently, which was one flight number, but it was a change of planes in MSP! Seems to defeat the purpose. Of course, I only got one segment and slightly fewer miles than if they had credited DCA-MSP and MSP-ABQ.
That was actually my first thought. Realistically though, it hardly seems like it could reduce an airline's mileage liability enough to matter.