As of now it requires JavaFX runtime which has to be installed seperately along with the JRE. But going forward they might mostly bundle JavaFX runtime with the JRE.
I dont think its some sort of difficult/huge dependency to achieve. These days most of the OSs come with the JRE installed. You will not be able to execute java applications without the JRE.
For that matter if you look at other RIA technologies- all of the require some sort of external runtime to execute.