can anyone explain why MS windows update site[s]?

[JRC]

I've downloaded and installed all critical updates from this site:
http://v4.windowsupdate.microsoft.com/en/default.asp
which *scans* [when I revisit], and says there are no critical
updates available. Of course.
But when I go to this version of windows update:
http://v4.windowsupdate.microsoft.com/catalog/en/default.asp
I'm asked to scan manually, and I get a completely different picture,
showing 53 available updates and service packs. Why is this?
WinXP Pro SP1 just purchased.

JRC

 

[DL]

2nd Site simply shows all updates for the particular opp.system
It doesnt scan yr system to identify what is required.