They sell it in the US dollars because everyone else sells everything in US dollars: yes, even Iran, Russia and North Korea. It's not a gesture of charity or good will on Saudi behalf.
Why, I totally would. I just maintain the position of U.S. dollar as international trade currency is largely due to its dependability and domestic market volume, rather than far reaching conspiracy of international bankers.
Saudi have zero say here. If they break relations and declare jihad on America tomorrow, they will still sell their oil in U.S. dollars.
I agree that dollar didn't become an international currency because the bankers had foreseen the advantages. Its largely an artifact of WW2 loan repayments and stability. But it would be naive to think that they haven't realized the advantage yet and are not actively trying to keep it that way. China is just now getting into this game but not making much headway.
Even now some of the oil to India (from Iran especially) is being payed in rupees (albeit priced in dollars).
