IE6 has been deprecated since July 2010. Support for it fell off long before then. Even countries with heavy amounts of software piracy are using later versions

IE6 has been deprecated since July 2010. Support for it fell off long before then. Even countries with heavy amounts of software piracy are using later versions of the browser. IE6 is considered as important as IE5.5, that is to say, beyond dead. My guess is that it isn't intentional. It is a combination of modern browser features which are not supported in IE6 (like you say, might be certificates as well), rendering errors and a whole lot of JS which was written without IE6 in mind that can be executed. IE8 is available for Windows XP, that would be a better option.