I don't believe that this has anything to do with similarity to any Specialized bikes, disk brakes, colors or any other aspect of the Specialized product line. I think that this comes down to Choi and Forsman likely having signed employment contracts with Specialized that assigned all their inventions to Specialized during the term of their employment. If you follow that assumption, then Specialized don't believe that they stole anything from their current line, rather the they *own* the Volagi bike design/intellectual property under the terms of their employee contracts. If so, then they are suing Volagi for selling a bike that is covered by Specialized intellectual property.
What makes this unfortunate in my eye is that between the Facebook posting and the bike rumor interview, it seems as though they are incriminating themselves somewhat by flagging that they had the ideas while employees, or at least during their notice period.
http://www.bikerumor.com/2012/01/05/...it/#more-38592
http://www.facebook.com/volagi/posts/355322411151386