At the same time though, you are right in the market leading nature of it. That is, while building your business the opportunity might arise that you can shift what you are doing and that shift would open up your market to a larger opportunity. Alternatively you could choose not to shift and go for a smaller win.
Why I take issue with the original post is because it is basically saying, if it looks like there is a market opportunity to make a billion dollar company, don't take it.
Actually some do. The classic example is Google's founders - they tried to exit to Yahoo! for a million or so, but were turned down.
Perhaps "accidentally" is not the word. Of course, it's not accidental - tons of hard work is involved. But many people never dream of building a billion dollar business, and a few of them still get there.
More importantly, focusing on building a billion dollar business might not be productive. It might actually distract you from doing what customers would like you to do.
The key point though is that, somewhere between their Yahoo pitch and today Sergei and Larry made the decision to grow to the $B scale. I think it was when Eric came on actually was when that shift happened.
Mojang?
So it wasn't an accident, as it happens it lined up so that interests aligned for the buyout.