I doubt that China and India are paying full price for oil. No way does a China or India have the ability to pay full price and in cash. They supply something that Iran, Venezuela, Arab countries want and get a discount. That something is cheap consumer goods and advanced weaponry. Not stating proven fact, this is my theory.
China and India do pay full price and cash for oil - it's one of the biggest expenditures of government. India doesn't really make advanced weaponry (just starting to do so now - definitely nothing sold) - it obtains weapons from Israel, France, and Russia. China makes weaponry, but it isn't great.
Actually, Asian countries (China, India, Japan, and the rest) pay *higher* prices for oil - there's a small surcharge (well, small in percentage terms) imposed on oil sales to Asian countries - I'm not sure of the reasoning behind it but it definitely exists.