I hate to seem callous here, but, that might've completely made sense. God forbid if Allen had died, the company, still pre-IPO startup whose main product was MS-DOS (pre Office or any version of Windows) would want its shares controlled by people with business interests in the company. When you are a startup you want to align incentives properly and yes, people who are unfortunately unable to contribute, even if it's through no fault of their own probably shouldn't have huge amounts of stock.
Besides that allegation I don't really know what else here is that negative on Bill Gates.
edit: MS-DOS not MS-DOC. Mistyped