Username or EmailPassword
1. The Live! version come in a auto-extracting archive, so you won't have to install anything to extract it. If you don't use Windows but Linux, you are supposed to rename the file cutting the '.exe' and leaving just the final '.7z' extension, and there are 90% chances that your distribution's file and package managers will be able to handle it. If you're using MacOS, than you'll probably have to spend 5 minutes of your time to download 7zip.
2. As other said, 7zip is open, free, and produces smaller archives than classic zip. Smaller archives means also minor download time, minor spent energy, and also minor bandwidth used to transfer the file. A difference of a few dozens megabytes over a 700 MB file might seems small for a single user downloading it, but when downloads are some thousands, they turn into many gigabytes or even a terabyte off. I think you can easily figure the economic and ecologic gain of it.
3. I can't exactly understand why a person that makes downloading of a single program a problem, should download and install a whole new operating system that will bring him the necessity of learning everything from scratch. You have issues downloading and installing a little, simple, tiny file decompressor... what will you do when you'll not find your 'explorer', your 'firefox' or your 'opera' anymore?
4. Your trolling about the 7zip issue had success: nobody actually talked about the distribution, about AROS progresses, about all the efforts we put into this, but you succeeded turning this thread into a compilation of obvious answers. All this with a pathetic rant about a compression format. Applause.