High-speed shimmy is an interaction between the bike and the rider.
The less trail the bike has, the easier it is to trigger it.
90% of frame mfgrs stupidly put steeper head tube angles on their tall frames, which reduces trail, making them more prone to shimmy.
(You can also put some blame on UCI for their front-center limits.)
Excellent articles on the topic:
http://davesbikeblog.squarespace.com...e-visited.html
http://velonews.competitor.com/2010/...-poorly_121162