I went to the official Dakar site - their rationale for the speed limit and why it would not be a prob is pretty much what we've surmised here - they already have a speed limit through towns and the Dakar is more about navigation and such than being able to fly through the desert at fantastic speeds.

Ach. Reading the stuff on the site was so inspiring. They seriously give bikers good value for money - the entry fee for a bike covers a lot more than the fee for a car. They also give great discounts for "amateurs" and loads of support. It looks like they're bending over backwards to give you the greatest time of your life.