Last trucks I drove had a cruise control so set it at 56mph and that's exactly what it did. This is why lorries can stay relatively close to each other in the inside lane.
To answer Loo's question about how people can video it,. It was obviously filmed from the opposite carriageway. Would you have pulled over onto the hard shoulder and ran across 3 lanes of motorway? I know I wouldn't.
What about TV crews who video dreadful things every week? Are they any different ? Ok I'll admit they usually film things after the event, but it's not unknown for them to be on the spot when something major happens. Should they stop filming to help in some emergency?