Concerning the updates Vista's Setup pulls down before installing

(When not installing from booting the DVD, of course.)

Is there any record of what the heck they are? Is the March application
compatibility update one of them, for instance? It was never available in
WU to me post-install, and trying to install it manually leads to the
cryptic message "The update does not apply to your system." So was it just
slipstreamed into the install and rendered invisible?