The more I look at this the more puzzling it becomes, it is hard to believe that Microsoft is motivated purely by jilted feelings which is not say that they don't play a part.

This analysis makes sense too
"In dropping this first patent bomb, Microsoft has clearly signaled that it is willing to use the FAT patents to prevent competition," Dean told LinuxInsider. "Now it's a real threat to Apple and Sandisk and TomTom, Nokia (NYSE: NOK) , Motorola (NYSE: MOT) and every other company that uses most flash formatted devices."
by Kevin Dean taken from the piece on http://www.linuxinsider.com/story/Mi...War-66338.html

From what I can see it is Microsoft's intention to a) enforce its FAT patent and/or b) to break TomTom

Bruce Perens attempt at analysis doesn't seem to come to a definitive conclusion either except that the industry should move to open and non-patented file systems.
http://itmanagement.earthweb.com/osr...om-Lawsuit.htm

Perhaps a good consequence of the TomTom suit may be to force this to happen.