It's the way the stators are wound.
http://www.mmsonline.com/articles/wy...in-perspective
http://www.roarracing.com/downloads/..._Rule_Book.pdf [pg 49]
Roar Approved "spec" motors are Wye wound, which means the windings are inter connected to a common point, which is usually on the pinion side of the stator. Since the connection to the speed control is at the other end, you end up with an extra 0.5T building the motor.
The "even" turn motors you asked about are Delta configuration windings, but would only be legal in mod.
Since a Wye motor can run just fine sensorless as well, there's not a whole lot of incentive for manufacturers to make both winding configurations.