It already is. You can buy certificates from VeriSign, Thawte and others. It's rather a pain, though — you have to verify your identity to them (otherwise they can't certify it) which means using a notary or something similar. Also, certificates are expensive due to a chicken-and-egg situation, since they're currently mostly used by businesses, not consumers.

The whole business of Public Key Infrastructure (PKI) is pretty convoluted. I recommend reading Schneier's "Practical Cryptography" for a good overview. It's one of those areas, like AI or the "Semantic Web" that's prone to utopian ideals that collide against messy realities.