My guess is the Jamis' forks have some device to prevent the axle being pulled from the fork under braking. It maybe a shroud, an extra aggressive set of "lawyer's lips" or some other device. Whether the fork is curved or not is not really the issue. Forks designed for disk brakes generally are more rigid and may have a thicker walled tube or a larger diameter tube on the rotor's side. More recently a through bolt design has been used and may become more popular in the future.

You may want to discuss axle retention with your builder if he hasn't provisioned for this.

Brad