A good point. They don't even mention connection reuse information leaks, for instance if any one URL sent to google analytics contains fingerprint information then all URLs sent over that same connection belong to you as well, as the network connection is kept open a long time and reused across all domains. I wonder if they are aware of the problem or just didn't mention it.
Now that Google has pushed HTTP/2 on everybody, connection reuse will be a major new fingerprinting and tracking technique because it keeps connections open a long time and essentially can't be proxied so one connection is always one browser.
You might want to pay a lot more attention to SSL-based tracking methods, e.g. https://sites.google.com/a/chromium.org/dev/Home/chromium-se...
Uncoupling your use of Google services from your other online activities is much harder than many people seem to believe.