As a (very very minor) shareholder, I'd rather pay for that than Google+.

Protecting a journalists free speech is in line with the original do not evil motto. It's also great advertising for GCE capabilities around handling DDoS.

Google probably has excess capacity. There is nothing more to be paid if the server is sitting there doing nothing. It's actually good for Google because they get to analyze a huge amount of traffic which they can use to protect paying clients.