Your points are all valid, but many of these apply to other industries too, and other industries also have their own subset of problems.

You could basically sum it up by saying 'Startups are risky. Angel Investors are brave'.

All the risks are why Angels/VCs (including PG in his essays) are always saying they look for promising founders rather than good ideas. There are so many risks that can derail a great idea, what's important is that you can trust the people at the wheel to make the right moves.

There are a lot of technical problems in making a game, but if John Carmack is doing the coding, I'd trust him to solve them. There are a lot of gameplay problems in making a game, but if Soren Johnson is doing the design, I'd trust him to solve them.