Microsoft sealed their fate in making it a closed system
There's nothing wrong with a closed system take a look at the famous (in the IT security industry at least !) Sidewinder Firewall for example, it's been around for ages (1994-ish) and the number of security advisories issued against it's name can be counted on less than one hand.... and amongst those limited vulnerabilities, I think you would be hard pushed to find one that would allow you access to the network behind the firewall.
