There needs to be some balance between discoverability and usability. The most discoverable interface, after all, is a black screen that does nothing. It doesn't do anything, so it's easy to learn. It's also completely useless.

Remember mice before they had scroll wheels? Neither do I -- my brain has blocked out that painful memory. (It may have been "hard to learn to use", but once you learn a simple motion it makes every day significantly easier. Multi-touch may be similar, or it may not be... I can't say since I avoid the mouse now.)