1: I'm curious about this one. Maybe they're concerned people won't know what's going on if they're falling relentlessly fast. It's frustrating in Skyrim when I die from falling when I don't feel as I've been falling fast enough for death. HOWEVER: Mirror's Edge gets this right. When you fall, it's scary.
2: It's a trend, it'll change.
3: The game is not about running around in a realistic night. Otherwise, it would be too dark to do much of anything (this is why most people sleep at night). Night is usually used to make the world seem dynamic, or to enhance a scary situation (HL2 - Ravenholm). The Thief series gets this more right and it's really fun, but it's not for every game.
4: Which would you prefer? seeing two rag-dolls sometimes clipping through each other, or 20 frames per second. Think about it.
5: It's probably a choice of immersion. I'm sure some gamers would see bodies and arms in their screen as a weird addition to the HUD that they don't need. Also, there are two weird things with seeing legs. In L4D, when you see legs, you look down and they look reallllly far away and reallly long (because of the way we see things, we actually TONS more than a computer screen captures). Finally, it's hard to make the legs not clip with dead bodies, stairs, and stuff. So there is also that.