No, it's due to so many intranet applications being written as one-browser hacks completely ignoring standards.

Mozilla has had similar issues with intranets (though not to as large an extent, due to their smaller install base), and you can't exactly blame _that_ on lack of standards support. What you _can_ blame it on is things like people writing intranet apps that depend on the user flipping some hidden pref in the browser to relax a security policy and then breaking when that pref is later removed, say.

Funnily enough, we had a similar problem at one of my previous employers with Firefox 3.6.

If an institution sticks doggedly to one version of one browser, then it stands to reason any intranet software is going to be optimised for nothing other than that.