many reasons for not updating IE
I only use IE in windows on a virtual machine to test the kind of mess it makes of my web-design. I have to test IE5, 6 & 7 as each version make it's own particular kind of mess. No doubt IE8 will introduce some new hellish experiences for web-designers.
Being as the wretched programme is an intrinsic part of the operating system, I would never allow it to connect to the internet on a non-virtual machine. I would never let M$oft update it & mess my system about.
My golden rule is never allow any M$ programme to connect to the internet. Use a non-M$ firewall & you can probably get away with using windows.
After applying sp2 to my virtual XP in order to get IE7 & seeing just how horrible the whole process is for XP windows users I have no surprise at all that people don't bother to update.