I'm wondering how many of those who drop out of college to start companies succeed -- and by success I don't mean Zuckerberg or Gates type of success but have a profitable company and make enough money to live a comfortable (not extravagant) life?

I believe college is not for everybody or at the same stage of life (i.e., you could go back if the company you started doesn't work out). But I do agree with Thiel's point that a degree provides some level of insurance.