If you haven't had a look in the Music section of the iTunes App Store recently, do. Mixed in with a multitude of other types of apps are quite a few that are essentially new instruments, some quite unlike any physical instrument in existence.
In my humble opinion, this is a good thing! I've been collecting instrument apps ever since the App Store opened, and very much enjoying going through them. (It also turns out to be a good way to introduce others to the iPad!)