Exactly and that is the number one reason folks get hurt on extension ladders....kick out.
Yup, I set my ladders so straight up it scares people, but I've never seen one go over from the top, except in the movie Animal House. A couple of problems with the ladder on such little angle is it makes the top where it rests against the house is prone to easily move side to side, especially on a gutter, (metal to metal). Also if your in a sticky situation and have to push against the top of the ladder to reach up onto the roof higher you need to have the ladder on a greater angle with some one holding it or it tied off at the bottom.
But those videos are stupid, even though I'm no fan of those fold up ladders I don't think they are any more dangerous to use than any other ladder.
I've never tested them but I don't think there would be any greater risk of kick out because of the slack in the joints. It is critical to never step on a rung or push on the ladder above the ladders contact point at the roof edge.
The transition of moving between the ladder and the roof is the most dangerous thing involved with ladder use. Leaning on or pushing on the section of ladder above the roof will almost guarantee the bottom to unload. That's why on any hard surface, even if perfectly level, the bottom should be secured if you are getting off the ladder at the top. On soft surface the bottom can be stuck into the ground which helps prevent kick out.
There is an OSHA requirement of 3 feet minimum above the edge of the roof, but that is a bit of a double edged sword, it is designed to have a hand hold for that transition, but also is lever that is trying to move the bottom of the ladder. A local roofing company employee was killed in a fall a couple of years ago, part of the blame was the ladder was not high enough over the edge of the roof.
I've been working with ladders all my life, you can never become complacent when using ladders. It just you and gravity up there. So far there is no OSHA fall arrest requirements for portable ladders. there is however for fixed ladders.
JB