|I told you why already. A service pack is a rollup of ALL the updates, etc. since the release of the OS or the last service pack.|
The CDs you are referring to obviously have differences. Just because both have SP2 integrated doesn' mean they are the same.
SP3 was 153MB in size. Some or most of those files may have been included in the larger version. Even after SP3 there were/are many more updates that have been released. Most every week there are some, even now.
Microsoft is not going to press a new batch of disks without including the available updates. So, naturally something two years later is going to have many more updates included.
Go to Add/remove programs and look at all the updates that are on your system. Be sure to tick the box to show updates.