20 hours is definitely possible...
Stiglet, Mr Angry and others... The article says "Work for 20 hours without rest". It does not say "20 hours FDP without rest".
My airline regularly have me working for 20 hours without rest. We would normally check in early for a 12-13 hours FDP, sometimes with the 1 hour planned extension. After the flight we are positioning by either train, taxi, flight (or a combination) to another city. Thus extending the total duty to around 20 hours. We will then check in to a hotel for a 20-26 hour rest period. That means going from either day duty to night duty or vice versa. Then we do the full thing once again...
While I agree that the last couple of hours is not a Flight Duty and thus not a safety issue in itself, it does have a very large effect on the long term fatigue. A duty cycle such as that takes me days to recover from. My sleep pattern gets disrupted and my intestinal rhythm gets disturbed. With small children at home it gets even more difficult to recover during your Off days. (But of course... Pilots should not have families)