Win XP can run IE8.

Sometimes there are legitimate reasons like a legacy app that only works on IE6 that would be very expensive to time consuming to rewrite... however IE8 has compatiability views so really it comes down to lazy network/sys admin's who can't be stuffed upgrading/testing.

Win XP is over 10 years old and near end of life, people are going to have to upgrade/update sooner or later.

IE9 won't run on Win XP as it lacks the hardware acceleration api's needed.