This is what DRM* does. It makes you dependent on a central authority when you want access to things you paid for. It means that if a company goes out of business, or just plain gets bored of running a service, you lose access to everything you bought from it.
It can happen at any size. When Google decided that YouTube was more successful than their own video site, they shut down Google Video. And then had to be pushed into refunding people for videos they could no longer play. When Microsoft shut down MSN Music any music that had been bought from them ceased to play. The company suggested that people burn their music to CD and re-rip it to work around their own handcuffs.
If you're walking into a situation with your eyes open, then go for it. I pay money to Spotify on a monthly basis because I view it the same way I view cable TV - I'm paying for access, I'm not purchasing something. But if you want to keep something long term, and have it work the way you want it to**, then don't buy it unless it's DRM free.
*Digital Rights Management. Encrypting the data so that it can't be copied around, and can only be viewed/played through something which is authorised to do so.
**For instance if you decide that you'd like to switch away from a Kindle to a different book reader then, well, good luck, unless you're happy to find some software to strip the DRM off for you.
Original post on Dreamwidth - there are comments there.