Well, i completely agree with this but there is a problem: users. Many windows users will always have IE 'cause they are afraid installing new software or they even can't do it. Or they are contented with their browser and nothing better don't exists for them. (From their point of view.) Also a common user has no idea about how internet works and if you'll try to explain him what is xhtml or <object> you'll probably not succeed. Unfortunately, I know a lot of such people.
According to IE problems & bugs I use xml rather than xhtml/html.