It is entirely possible for Google to have an outage that takes down GAE and G+. Given that reality, it makes sense that their "emergency public communication" should be as separated as possible from their own infrastructure.

This makes twitter a very natural choice.

Bazinga! But below the belt, given the circumstances. I'd like to encourage engineers like Zafir to make themselves available to us (outside of google groups) more often.

The Twitter feed predates Google+ by several years.

Way to encourage open communication? Who cares what platform they use as long as they are posting updates, that's better than most sites.