The longer name is really what the list is named as far as Mailman is concerned. It is a very common request to have only the shorter name show but it is not possible with the current version of Mailman. We have some custom patches in development that may work for this, but they are not very close to being ready to use yet.
Mailman cannot have two lists with the same name (ie, discussion) at two different domain names so we allow it by simply appending the domain name to the end. It's not the most elegant setup, but Mailman does not allow anything much better. The next version of Mailman in development will have the features we need to do things nicely.
- DreamHost Head Honcho/Founder