I don't agree. Not every developer is an super genius who only solves problems using incredible feats of intelligence.
I learn something new everyday. For a learning experience we launched a new site using only HTML5. That was a fun learning experience, but it wasn't a really hard problem. And yes, it is part of our core mission.
Another example is how our company is always looking at new technologies. The concepts can be challenging and fun to learn for a developer. A couple of the more recent ones we've used are MongoDB, Node.js, PhoneGap... I'm sure there's more. Oh, right... we're building our first Rails 3 site. Now that's fun!