GPG makes a big deal of doing its own thing and trying to avoid "standards" which they believe might be tainted? It's very unclear to me. For smart cards, GPG wants to own the card completely, and does not want to play with anybody else or use the existing PKCS standards.

So it turns out that the "standard" email encryption is actually S/MIME, and it works pretty much everywhere (non-webmail) out of the box, with fairly decent UI. It even works on iPhones.