Since the vast majority of sites with Google CDN references are referencing it via http:// http://, using an unnecessary https:// https:// reference on an unsec

Since the vast majority of sites with Google CDN references are referencing it via http:// http://, using an unnecessary https:// https:// reference on an unsecured site eliminates most of the potential for cross-site caching (which is probably the biggest advantage of using a popular CDN like Google's).