In fact, the winning driver can now do an in-car celebration of just about any sort. Stopping on track, picking up the flag, or just about any other creative celebration is now legal--so long as it doesn't endanger fans or officials, "call into question the legality" of the car, or delay the podium ceremony.
The new exception to the rules after a race are likely attributable directly to Sebastian Vettel's antics last year. After winning the Indian Grand Prix at Buddh International Circuit last year, Vettel celebrated with a big cloud of donuts. Then he was fined a bit over S$40,000. But then Vettel, joined by his teammate Mark Webber, did donuts after finishing 1-2 at Abu Dhabi--essentially flipping the bird at the FIA's fines.
That left the FIA with the choice of looking like irrelevant, party poopers, or amending the regulations to allow some reasonable demonstrations of the joy of winning. We're glad they finally came around.
Lets hope we get to see some F1 donuts in Singapore this year.