I agree with your theory, though maybe not so much its implementation.

The coolest thing I've ever built was indeed something I was "told" to create as a part of my job. That doesn't dilute the fact that what I created took lots of creativity, careful thought and developed into an elegant, scalable solution for the problem at hand. I was very passionate about building it.

I think your litmus test is correct, but I think that regardless of _why_ someone built something, it's fairly easy to tell if they're passionate about having done it.

That said, the good ones almost always build things to scratch their own itch. Those things just may not be the coolest things.