Gates: one operating system to rule them all

In an interview with Spiegel magazine, Bill Gates pushes

his view of computer security: one company, one operating system: "The truth is: the fewer operating systems there are within a company, the better it is from a security point of view."

He goes on to once again slam the open source software movement, insinuating that the only way to solve security problems is to throw "billions of dollars" at it: "Our company has an unbelievable number of people who are solely responsible for this type of security around the clock." (a phrase comes to mind: "There is evil there that never sleeps.") Yep. It is pretty unbelievable that they're throwing billions of dollars and an unbelievable number of people at security issues and are still
failing miserably.

Bill also espouses the "security through obscurity"
myth that has been further debated here recently. Reader Brian
summed up the differences in OS philosophy thusly: "It's the difference between having a firewall with all ports open, and closing them as exploits become known
(RPC, MS-SQL, etc.) versus having a firewall with all ports closed and only opening the ones you need (if any.) That's the fundamental difference." There's that, and the fact that the
root user is disabled by default, that any malware damage done would only affect the current user, as well as the fact that any potential malware would need to get permission from an administrator to be installed in the first place (whereas Windows allows such malware to execute in the background)... to name a few.

Bill is blowing smoke. Feel free to riff on both big questions here: are you better off in a homogenous or a diverse OS environment in terms of security? As well as: Does a proprietary software company have an inherent edge over open source software in the realm of security?