Yeah no recent update to the update itself.
Update: I've now come across an xp 32bit machine which required the update, as far as i can tell nothing has been installed on that machine for over a year? Outside updates. Well that blew my theory on it missing the 32bit version over having the 64 bit version installed.
If anyone's interested it's update KB973923 we are talking about, all of a sudden it installs after being available for years and seems to without any recent install to trigger it either.