[CentOS] Why CentOS 5.2 is so large?

Hi, folks.

I have download the DVD image of CentOS 5.2. Comparing with the DVD
image of Upstream OS Provider, I got a surprise:

The size of the DVD image of Upstream OS Provider is just 2.87
GB(i386), but the size of the DVD image of CentOS 5.2(i386) is so
large that is 3.74 GB!

I kown that CentOS's developers did very excellent work on how to make
the Upstream OS more availability and add many good free software on
the CentOS. But where can I got the change or add list of CentOS? and
why the size change is so large? I think it is very useful for my
farther employ of CentOS.

Thanks!

(Yes, I can read the ReleaseNotes, but it is still can not disabuse
me, the secsion of "5.6. Packages added by CentOS that are not
included upstream" is so little.)