which is perhaps why he can "write as he talks", and get away with it. He honed his craft. I work with a few programmers who write exactly as they talk, and it is littered with misplaced, dangling modifiers, and misspellings of things like "bury the lead" vs "bury the lede". The overall structure of arguments is haphazard too. Writing is hard, and I think the best way to get better is to write things that you _want_ to get taken more seriously than just as if you were talking.
He can get away with it because he founded the company that owns this well-respected discussion forum; he can say whatever he wants and people will at the very least read it. It is a credit to his hard work in the industry and the even harder industry of online community-building that the community surrounding Y Combinator can sniff out a truly bad essay like this one (especially difficult when so many of his essays are so excellent) and call him out on it as they generally have here.