The main reason why Vista and Win7 updates seem to take a long time is the fact Microsoft has bundled many updates together. If you watch your status of your internet connection while observing the update progress, the download will pause for several minutes. The reasoning why this happens is there are a set of updates that are installing in the background, in which the trustedinstaller.exe is taking priority. The download will resume until it reaches a set category of updates that need installed before other updates can be. Rather slick actually.
If you would time the whole process vs. the XP process. I'd say its about the same. Plus this process will be painstakingly long if you are updating from a OEM install image or installation disc.
If you are really worried about this you can slipstream your Vista or Win7 installation images with redistributable service packs which are available on MSDN TechNet.
Hope this quiets down the controversy.