I suspect different teams are involved with scanning for malware URLs in Skype and implementing core OS protections, so the tradeoff you imply is illusory. Bes

I suspect different teams are involved with scanning for malware URLs in Skype and implementing core OS protections, so the tradeoff you imply is illusory. Besides, Microsoft already puts a lot of effort into the security of Windows, with seemingly good results. There's nothing wrong with defense in depth.