I'd be stunned if it was about money, he's the highest paid player at Real Madrid. I don't see money as a motivation for Ronaldo, never has been so far in his career anyway. He moved to Madrid because it was his dream to play for them which, being Portugese, is understandable. It wasn't about the money.
The media have no idea either really, they're only guessing logically.
Personally, I think it's to do with Iniesta winning the Best Player in Europe award. Maybe Ronaldo thinks he deserved it (debatable) and is sad that he isn't getting the credit he deserves. Just an idea, nobody knows the real reason yet.