Are Diablo 3 saves stored in the cloud?
Yes. They must be, in order for you to be able to log in from multiple locations and still have access to your characters.
Your character is represented by a database stored on the Battle.Net servers. Whenever you login, your character is "created" from the information in that database. So yes, you can login from any computer and access your character. That isn't quite the same as most games where your save is a file and it can be stored on some "cloud" computer, but it has similar effects.