That seems pretty reasonable within a datacenter. Nobody(?) would encrypt traffic from local client to local mysql server. But accessing remotely over network

That seems pretty reasonable within a datacenter. Nobody(?) would encrypt traffic from local client to local mysql server. But accessing remotely over network links that could be tapped by governments or other antagonists? If you had dedicated netsec and infosec departments as big as Facebook's, you might encrypt that. Some of the companies named in the PRISM slide deck are in a state of constant information warfare with hostile governments (like China) and governments openly desirous of tapping all networks (like India). They are also continuously beset by piratical criminals from all over the world. It seems unreasonable to assume that they would transmit data over long-distance links in the clear. I'm not saying they do encrypt everything or even most things. But as the basis of one's theories about PRISM, it doesn't seem like a good assumption.