I see this being correct, because if you stop, you are "giving back" a couple of knots that you had from taxiing onto the runway. That is, the static takeoff must overcome the total inertia of being at a standstill. Given that prop power is more or less instantaneous when applied, those few knots and already being in motion could be worth as much or more than starting the t/o roll from a stopped position with t/o power already applied. (Obviously N/A for a jet, where idle to TRT takes several seconds.)

I believe I'd instruct whatever the AFM/POH says, since I can't mathematically prove either one, and the Practical Test Standards say the applicant "applies brakes (if appropriate)", which could only mean "appropriate to that aircraft."
Zach