Rhodes is released under MIT license as well as some other components like RhoConnect. You can see more details of this at http://docs.rhomobile.com/rhodes/introduction#contributing
RhoElements (the bit that needs a license) is not distributed under MIT. If you create an app which uses pure Rhodes APIs (as defined at http://docs.rhomobile.com/rhoelements/apicompatibility and are considered to be non-enterprise) then it's free.
Yes... we are going to simplify this moving forward!!