Integration of Internet Explorer and Windows: Information From Answers.com: "There are a number of significant vulnerabilities in technologies relating to the IE domain/zone security model, local file system (Local Machine Zone) trust, the Dynamic HTML (DHTML) document object model (in particular, proprietary DHTML features), the HTML Help system, MIME type determination, the graphical user interface (GUI), and ActiveX. … IE is integrated into Windows to such an extent that vulnerabilities in IE frequently provide an attacker significant access to the operating system."
Anche il resto dell'articolo, tratto da Wikipedia, contiene spunti interessanti su come si può, almeno entro certi limiti, rimuovere IE da Windows XP e da altri Windows.