Keep in mind that the source code is provided with the GetGRSSDKP.exe program. It's in GetGRSSDKP.pl (it's perl code). Also included in the readme.txt are the instructions to compile it to it's current form.
This is the extent of what it does:
1) You enter the address of your guild's site and click "OK"
2) It downloads the latest luadkp.php and saves it to GRSS_Data.lua
3) It reads the GuildRaidSnapShot.toc file for the version of the mod you are currently running.
4) It reads the file
http://www.dkpsystem.com/grssversion which contains the current version number.
5) If the current version > version on your computer, it asks if you'd like to update to the latest version
6) If you press "Yes", it downloads new copies of the mod (.lua, .toc, .xml, and .txt files).
The code is kept intentionally open for those skeptical.
I understand that people are skeptical of exe's included in Addons, which is precisely why the source code is included. But running the EXE is so much easier than manually downloading it.