Don't know about the rest of HN but I found it strangely reassuring that even someone as talented as DHH can end up in front of a white board during an interview and feel stupid. I've been there...
He's obviously very talented at design (not necessarily only UI design but general program structure and framework design). But if you needed someone to write packet routing algorithms or design a high-availability database engine from scratch, that may not be his cup of tea.
OTOH, I bet there are developers who love brain teasers and puzzles who may very well excel at that type of work but couldn't implement a huge software system with many moving parts without having it collapse under its weight.