[asynchronous13]

It's legacy.

The FAA has a distinction between commercial and recreational flying. When the laws were written, commercial meant that you were carrying passengers in a full-sized aircraft. And it makes sense to have more rigid rules in place for passenger aircraft.

Times have changed and using commercial vs recreational doesn't make sense anymore. The FAA is trying to apply existing laws to new technology. So, we're left with the case that it's perfectly legal to put a camera on a toy RC aircraft and take pictures for fun. But if you sell those pictures now you've crossed into commercial territory and your flight was no longer legal.

edit The good news is that the FAA is working on new rules. They're just miserably slow about it.