The decision to create a new forum is explained in the forum itself. But I can explain it here, too.
The jQuery Showroom is dedicated to the jQueryAdmin module and the plugins that are packed for it. Nearly every discussion concerning this module leads to flame wars here in the WB forum. So it's nearly impossible to support the module and any questions related to the jQuery Plugins that are packed for it in the WB forum without annoying the users.
In addition, it seemed from the beginning that jQuery related discussions are not really welcome here. It's simply not a WB subject (like FCK isn't). This is a very personal impression I am not going to discuss.
So, I (and some others) thought it would be better to discuss jQueryAdmin and jQuery related questions where the plugins are located. "Erpe" supported this by creating the Showroom Forum.
If you are interested in more details, feel free to contact me by PN.