The world’s two proviersof satellite radio agreed to merge, vowing to endtheir brutal battle for customers and to work together to persuade more people to pay for a medium that most use for free.

In implicitly acknowledging that the market can’t support two such services, the deal also posed a bigger question: Can it support even one?

More than 80 million people listen to AM or FM radio.Some 90 million people have iPods. About 65million people listen to Internet radio.Yet only 14 million have satellite radio receivers – and have agreed to pay $13 a month to subscribe to digital feeds of music, sports, and talk – despite the two rivals’ investments of billion of dollars in marketing and technology.