I get the feeling they don't bother testing on anything but super low latency, of if they do they don't care about a horrible user experience.
For me the super bad user experiences in this area have been greatly less, for me. Maybe they actually did something to address the problems (they are still far worse than any other sites I used, but still much better than they were for the last couple years).
I travel to rural areas in the South Indian state of Andhra Pradesh every month. The connection quality is as poor as its availability is flaky. I find that GMail, Google Drive and the Google search page always load. Business correspondence and collaborative editing have not been problems at all. I have not tried Google+, though. I shall try it the next time.
On the other hand, my biggest problems have been with GitHub. Not once in the last 18 months have the GitHub Web pages loaded. That makes reviewing and merging pull requests very painful. I reported this to GitHub long ago, but have not seen any improvement yet.