I personally never saw the police cruisers speeding as an abuse of power, but rather a logistics matter. If a cop went the speed limit on a highway, everyone else would pack in behind the cruiser, terrified to pass for fear of getting a ticket. Such a situation could turn dangerous situation kinda quick as everyone began to move in a huge clot behind the cop.

Out on the highway or interstate, a cop's job is to be seen. Visibility is what keeps people from driving like they're on the Autobahn.

I do agree that the running a red light using the siren is a total and pretty shitty abuse of power.

Update: British police pursuit drivers have standing instructions to drive either 10 mph higher or lower than the speed limit to avoid the 'bunching up' effect. I don't know if this is policy in the States, but it makes sense.
Thanks to Withnail for the info.