After searching the forums, I found that maybe it's just there because the 'Solutions' on my account require it.
According to this post;
http://www.webassist.com/forums/posts.php?t=19061&accesscheck=/forums/posts.php?t=19061
the 'Extensions' are all developer licensed so Power CMS (Solution) is good for one site and Power CMS Builder (Extension) should be good for as many as I need, correct?