No such rule exists in the UK.

There is a further exemption from the US rule when ATC inform the crew that repositioning to the gate would severely impact on operations. Not sure if this may have been the case with the EWR flight.

Sadly it is a pain in the backside. Some days carriers will simply cancel a flight, and some US carriers operate their crews into their version of discretion on order to recover a now empty aircraft to base and leave pax stranded. It works out cheaper than the potential fine.