There have been incidents that Google didn't acknowledge at all. There was one day where all sites using custom domains were redirected to Google.com for several hours, including their own Chrome Web Store. (which, I presume, runs on App Engine)
It eventually resolved after a few hours, but both during & after the incident, there wasn't any public communication from Google.
Well I can certainly hope they upped the honesty factor. (My experience is from 2010 & 2011. If the page you linked to is indeed the new version of the one I recall — is there no standalone App Engine status page? — then it’s certainly be massively redesigned.)
