The reasons are actually a lot simpler than you guys are making them out to be.
First, the majority of users out there are using Windows (and even more so for LotRO since it is a Windows only game) and a .zip extractor comes standard with Windows. They don't have to go find a .rar extractor to install. On that same note, the majority of users get a .rar file and have no idea what it is or how to deal with it. They understand .zip files though. They would be completely lost if they saw a .7zip or .tar extension!
The second reason, to be completely honest, is actually purely for our own convenience. It's easier for us to check a .zip file than it is to check a .rar file. There is a plugin we can use on our sites that allows us to look inside a .zip file without having to download it. There isn't an equivalent plugin for .rar files. Maybe not the most 'noble' of reasons, but there it is.
