He doesn't think that. Though he claims to have made good decisions and benefited from competitor blunders, he frequently refers to incidents that nearly sank the company, and acknowledges the good fortune that saved them and helped them to their very happy exit.
Where would Microsoft's shrinkwrap sales strategy have been without legal advice?
Edit: In 1980, she discussed with John Opel, a fellow committee member who was the chairman of the International Business Machines Corporation," her son's company. "Mr. Opel, by some accounts, mentioned Mrs. Gates to other I.B.M. executives. A few weeks later, I.B.M. took a chance by hiring Microsoft, then a small software firm, to develop an operating system for its first personal computer." http://en.wikipedia.org/wiki/Mary_Maxwell_Gates
The first is probably true, I agree atleast. Your second point about them not being heavy handed because they knew Bill's mother I just can't see having any shred of truth.
IBM also made a sweetheart deal with Intel with no mother's involved.
The reason they made those deals has been stated many times over.
IBM was in a huge rush to ship and they needed an OS and CPU in a very bad way. They made those deals because that's what allowed them to ship.
"Bill Gates is a smart, determined, and hardworking man, but you need more than that to make as much money as he has. You also need to be very lucky."
Or perhaps PG thinks his personal success is based purely off his own brilliance with no helpful outside factors needed (i.e. competitor blunders, etc)? :)