(1) is even lovely titled "California Pit Stop". Because people from California don't know to stop on the white line (or have a terrible perception of where the front of their vehicle is) many people stop in the pedestrian crossing. They proceed to roll through the 4-way stop so long as they don't see anyone. Although 20mph is cutting it, perhaps 10-15? Either way they never come to a full and complete stop.

(2) is because seemingly nobody knows 4-way stops are FIFO and believe it's "Straights first then turns". If paths are non-conflicting, both people will go at the same time.

(4) is only partially true. If you're in a rush, left-signalling is not necessary; it's user discretion. Also all straight/right turn lanes are assumed to be straight, since nobody signals right turns. This is a reminder that it is your fault for not turning right due to potential oncoming traffic and the car behind you will occasionally honk in irritation that you didn't pull out in front of traffic that was potentially continuing straight.

Driving in the L.A area is hell.