Paul Graham wrote an interesting essay "Why There Aren't More Googles" where he basically places the blame on reluctant VCs who won't invest small amounts on tiny startups.
So what's the real reason there aren't more Googles? Curiously enough, it's the same reason Google and Facebook have remained independent: money guys undervalue the most innovative startups.
The reason there aren't more Googles is not that investors encourage innovative startups to sell out, but that they won't even fund them.
There is a Capital Gap between the $50K from Friends and Family, and the $3M to $5M from VCs. But, that gap is being filled by Angel Investors who invested $26B in over 57,000 companies in 2007.
How many Billion dollar ideas are there? Angels in vested $26 Billion in 57,000 companies last year, while VCs invested another $29.4B in 3,813 companies in 2007. The problem isn't a lack of capital, or even a lack of entrepreneurs. It is a lack of disruptive big ideas that can generate a Billion dollars.
Most startups are acquired before they reach $1B. Look at the M&A numbers over the past few years. Last year there were $25.4B in M&A transactions compared to just $10.3B in IPOs.
Paul Graham and Y Combinator are hatching some really cool companies. Is there a Billion dollar company in there? Certainly there are some $50M ideas, but a Billion? Possibly, but unlikely.