I was told that the CHP actually gives their motor officers the choice of which bike they ride. It's not a mandatory "this is the bike you'll ride - period". The primary reason that CHP began riding the BMW RT was the ABS, not offered on the Harley Davidson until 2007(?).
Many Police Departments allow the LEOs to choose from a variety of bikes. For instance, in the city I work in (Salinas, CA) the PD motor officer are riding BMW RTPs, Honda ST 1300s and Harley Davidsons. I haven't spoken to any of the LEOs about their choice in the matter but presume that the officer has a choice in the motorcycle he is assigned to ride.