1) Their sample data is based on your product usage and people who use rescue time are probably heavy cloud users. So population set is unfairly waited toward the cloud.
2) Microsoft's get's the majority of their users and revenue from enterprise level sales. Google customer on the other hand is primarily the consumer and small business. This is important because in most enterprise level environments users can't install an application like rescue time.
3) Lastly people double dip - at work use outlook for work and gmail for personal.
It would interesting to just look at productivity apps like word processing or presentation with referrer values from .com addresses only (not logins) . The trending might be very different.
And goverments and public institutions around the world