So, Bill Gates claims Microsoft software is superior to open source offerings because it is more interoperable. That's a convenient attack, considering the following:
1) Microsoft has deliberately, through patents as well as a combination of secrecy and rapid changes, foiled efforts at open source software interoperating with its products.
2) Microsoft refuses to incorporate support for standards whose origin is in open source software (like OpenOffice document format), limiting their uptake.
So yes, Microsoft software is more interoperable with the existing install base, simply because it has taken steps to ensure a competitor cannot claim that title. Does that say anything about the quality of Microsoft software? No, but it does say something about the assumptions their business model is based on, as well as their attitude towards cooperation and open standards.
A security hole with a patch reflects badly on a vendor because the security hole existed in the first place.
A security hole without a patch reflects badly on a vendor because they are not supporting their software.
Both reflect badly on the vendor, and neither should be apologized for by platform advocates.
A remote push vulnerability is worse than a remote pull vulnerability is worse than a local vulnerability.
A politician who has noble intent but ill implementation is equal in merit to a politican who has ill intent and solid implementation.