The difference is you can choose what you hear with the internet stuff most of the time, and skip songs. all other radio stations don't have the skip function. Makes sense they'd have to pay more if they are offering the ability to chose exactly what you hear most of the time.
EDIT: I'd like to see actual numbers over time for these guys, but Internet Radio should have to pay a higher fee as it makes listening to almost anything at any second possible.
Your edit makes no sense, why would you charge more money in that situation? I don't know about Pandora but spotify pays on a per stream basis so why the hell would you charge them MORE money for more plays? That could ruin these companies.