Great point and one that I think typical computer savvy users already do. It is in the security-expert-fantasy-world that the perfect quickly becomes the enemy of the good.
For example, using SSL to send sensitive data like passwords or payment info is nearly ubiquitous. Yes, there are many flaws in SSL's trust model, but the cost is so small, using it is a no brainer.
However, PGP encrypted email is much more rarely used. It has numerous higher costs, from special email software to the social pain of getting your friends to also use it. The benefit is still high, but the cost is high too and that results in far less usage.
In the real world, informed people look at the cost benefit break down of security. Just like we all don't drive semi trucks around even though they are safer in a collision, we all don't communicate in the most secure fashion because there is a cost associated with that decision. With that in mind, the easiest path towards greater security in communications population-wide would be to focus less on improving the security and more on lowering the associated cost.