I don't agree with what you wrote at the end. It's not a "mistake" to bootstrap and have a much higher probability of success with a lower possible return. I know that's probably not what you meant, because you wrote earlier that we could have been "more successful", but it also ignores what would have been a much higher risk and loss of ownership in your assumption.
Joel and I are naturally conservative in nature and having succeeded at Fog Creek with what we set out to do (building a successful company where devs wanted to work) allowed us to swing for the fences with Trello and Stack Exchange. The risk is much higher. The reward is bigger, but we own a lot less of those VC funded companies.