This statement is incredibly disappointing, given how much effort is done with other kinds of apps. How can encrypted communication not be a worthwile, and potentially lucrative niche?
I would, however, recommend adopting PGP, as that seems the simplest route to go.
A related point is that as long as the majority of people remain happy with such services, there is little push to make encryption easier. After all, if you've already basically made you email public, why would anyone think that you want to encrypt it? The popularity of Gmail and similar services is proof that there is no demand for such things.
There used to be a nice Firefox extension called FireGPG. It integrated with Gmail. I think it had a lot of potential but it died.