Gmail's receiving mostly authenticated email

Saw an interesting article from Gmail on their inbound email statistics. Over 91% is authenticated with either DKIM or SPF. 75% is both, the rest is one or the other. That doesn't indicate how much is encrypted, but anything that has the framework to do that authentication could fetch a key as well. (Doesn't stop the feds from collecting the mail after Gmail receives it, of course, but it's an indication of how much email could relatively easily add some encryption to reduce in-transit eavesdropping.)