According to Peter Kafka at Media Memo, Spotify reached this mark about a month ago, but is only now announcing it. This could give the company the negotiating leverage it needs to get the rest of the major labels, i.e. UMG and WMG, on board. One thing to consider, as the labels likely have, is that Spotify isn't just a marketer for itself. By introducing users to music streaming, it markets the idea subscription music in general.
Most people don't even know about the services that already exist in the US.
Since Apple and Google aren't looking to enter the sector, it will take a company like Spotify to raise awareness of the larger market. Even though Rhapsody is now offering 60-day trials of its service and receiving massive promotion through MTV, it remains to be seen if the company can climb up to Spotify level numbers.
Fan interest in subscription music isn't grounded in indifference, it's grounded in ignorance. Spotify could change that. And if Spotify can, its rivals may benefit.
(That is, of course, if the Apple Tax doesn't drive them all out of business.)
Subscription music has been attempting to drudge its way out of obscurity for almost a decade now, but a huge shift in consumption habits is still possible.
Clearly, fan interest does exist. 1 million subscribers and counting.