As a first responder, who has driven a variety of emergency vehicles including Crown Vics, Suburbans and Ambulances, let me say that you are failing to consider one side of the argument and being dismissive.
Firstly, there is the time-factor argument. Emergency vehicles are already forced to slow down for liability and safety reasons in a variety of situations, including stoplights and signs. In a world governed by response time figures, additional slow downs are not only political non-starters, they translate into real lives lost and real damage done.
Second, there is an economic factor for damage to vehicles. I've hit speedbumps in ambulances at near-Code speed, and you feel every mph in the barebones suspension of them. The wear and tear translates to repair costs, earlier replacement (of a $250,000 rig) and downtime meaning trucks either are left unreplaced while broken or alternate vehicles must be purchased and maintained again adding cost to a economically depressed city budget.