You may find this hard to believe, but when I started this was the only way to do upper floor windows. There were several companies all chasing the same contracts and prices were so low no-one could afford to use ladders/scaffolding/safety harnesses etc, there just wasn't time.
Councils were the worst offenders, I worked for a company doing all the Inner London schools, the contracts were awarded by the now defunct Inner London Education Authority. Their only criterium was price, so the cheapest quote always got the contract and that meant every possible corner had to be cut.
We never saw it as a problem - we would go to a job then work out the best way to get at the 'out of reach' windows'. This usually entailed climbing out of the window and standing on the sill. That ledge the man in the video is standing on looks to be about 2 foot wide - if a 'tumbler' (trainee) were to baulk at 'walking' it the experienced men would laugh and say "I could ride a bike round that"
I even had to train tumblers to 'jump' (our term for this type of cleaning) the upper windows and I would always say to them "If you were doing the ground floor, and that ledge was just a row of slabs on the ground around the bottom of the building, why would you fall off it?"
Standing on the sills was a bit more tricky, and we had an unbreakable rule "One hand for the job, one hand for yourself" You had to stand on the sill, balance by digging your fingers into the channel that the sash ran in (or any other finger hold) and clean with the other hand. (If there wasn't a decent hand hold then the job couldn't be done). Even for this method I would say: "If these windows were ground floor and the sills were six inches up and you had to stand on them to reach the top of the glass, could you do it without falling off?" I woud even make them do a few ground floor windows to prove to themselves they could do it.
I worked for that company for about 4 years and in that time I never heard of anyone on that firm or any other falling while 'jumping' an upper floor window.
I wouldn't (I couldn't!!) do it now and looking back I see the danger, but no-one forced us to do it, it was of our own free will and for 99% of the time the only danger was to ourselves so if we chose to take the risk we also accepted the responsibility.
I'm not going the claim that it was the right thing to do, or that we should go back to those days, but today the State is trying to take every shred of personal responsibility away from us which can only be a bad thing - we will all end up knowing nothing is our fault, the State should have prevented us from taking any risk.
PS I don't condone the man in the video doing what he did over a public street - he was putting innocent people in danger in the event of his falling.