Yeah they could have skipped chunks of it since all parts have per-component update. Also where is slipstream. Problem here is that the SP had to be released fast to help Vista users so no time for luxury of flexibility. Also Vista architecture is new, give them some time, they already said that SP2 will have slipstream, maybe it will skip missing parts as well, especially now when they see that it might be useful. XP Sp3 install might even work on a lite XP but then again I would not recommend it. It could return some parts. Even for a full OS it's best to reinstall when SP comes out. If reinstallation once a year is too much fuss then don't tamper with the OS.