Actually yesterday afternoon I updated the demo site and remved some older skins and added some new ones created with Artisteer 3.1. So currently the dmeo site has skins that are not available in the current release but will be in the next release.
We also ship an extraskins.zip file with each release that has older skins as well as some not so old ones. We just have too many to include them all in the main mojoPortal package. I don't like to put all of the skins on the demo site because some of them don't demo well or don't look as good though they might be a good start for a new design. The demo site is meant to show mojoPortal in its best light and if I keep all the skins on there it seems like the competition drops by to make sure its using the ugliest one ;-D