> "Which startups died because they got buried under the weight of their own codebase?" That's a long and very depressing list. In many of those situations, some TDD might have helped.

Could you give some examples? PG doesn't include that in his list: http://www.paulgraham.com/startupmistakes.html, and in my personal experience I've never met a startup that failed because they had an unmanageable codebase.