I can't comment on the 28mph top speed on the new models, but it was very easy to change the top speed on my 2015 Pedego Ridgerider and my wife's city Commuter to 25mph. Only took me a couple of minutes.
From rumors I've heard, Pedego is moving to 20mph top speed, rather than the easily adjustable 25mph system they've let out for years. Changing the top speed would require reprogramming or replacing the controller.