vilulf, uninstallers almost never clean up registry entries created by an installed program. (Un)Installers generally remove only what they've created directly. Programs often create files and registry entries when they are first run, which the installer knows nothing about, so... your argument is only argumentative. If you've never cleaned it up manually I can pretty much guarantee your registry is full of entries from long 'uninstalled' programs.
I posted message 57 on the game page regarding the 'installation' and the registry key, I will add that the key data isn't bloated and isn't anything to worry about deleting, any more than the junk from a hundred other installs. I also noted the clean and safe nature of this game and I'll second that statement here. No worries.
A note to everyone: I speak confidently because I monitor all software using system snapshot utilities, which allow me to see every change in the file system (files on the hard drive) or the registry (the windows database for program settings). I take a snapshot before and after installing a program and another set before and after running the installed program (and sometimes a snaphot after each of the first few runs of program). By comparing snapshots I can see what has been changed or added along the way, and am thus able to archive or delete all such things. I'd recommend similar tactics for anyone with moderate technical knowledge and a healthy sense of paranoia.
I was very suspicious of Giveaway of the Day at first, but was pleased to discover their setup files are as clean and well behaved as any software I've seen. Keep on keepin' on GOTD!