Earlier quoted context omitted.
The business model isn't there. I have yet to see a large group of consumers willing to pay for secure email and the only other alternative, advertising, leads to the exact same problem that you face with GMail.
+1 for willing to pay for secure email.
There is another problem, US govt' need to get access all these messages. For example http://en.wikipedia.org/wiki/Hushmail, people seemed to have signed up, but Hushmail was forced to provide plaintext messages to US govt upon request. So they sort of compromised their main selling point.
That is probably the largest problem, you'd be stuck between a rock and a hard place. You either please your security conscious customers or please Uncle Sam. You can't please both.