> You don't necessarily need a $5000 HSM solution to issue your own SSL certificates at this level.
Well sure, I can issue them myself in a few minutes, the issue is that arbitrary mail servers won't be able to authenticate me. Which means we're means we're back to MITM attacks—better than plain text if the observer can't manipulate the data stream—but I wouldn't bet on it. Work with the assumption that the NSA is Mallory, not Eve.
How is that different to the web of trust between friends that the parent referred to?
Of course there's no need to rely on a central CA - it's not hard to run your own, and you can make it reasonably secure - say, a small ARM Linux board with passphrase-protected private keys on a removable SD card. Generating the keys in a secure way is perhaps a bigger problem - untrusted hardware RNGs, poor quality entropy after boot etc.
One can also keep a virtual machine CA on a hardware-encrypted USB device (IronKey, say, depending on your level of trust with Imation) - it's easy enough to bootstrap a tiny Linux distribuution from source with just OpenSSL and some utility scripts to issue & revoke certs.
You don't necessarily need a $5000 HSM solution to issue your own SSL certificates at this level.