Why are airspeed gauges labeled above Vne?
I can think of several reasons, why you would want to have some extra room:


The fact that you should not exceed $ V_\mathrm{ne} $, does not mean you never actually do. It would be good to know by how much you are currently exceeding it, so you can decide how to react to this situation.
Not every aircraft model gets their own specific gauge. Cessna probably has a few gauges available and put the one with the smallest extra room above $ V_\mathrm{ne} $ on the aircraft. This is quite similar to cars, where you get the same speedometer on most models of a car, despite having different engines and thus different maximum speeds. It is simply cheaper to produce (and certify) only a few different airspeed indicators.
The aircraft's $ V_\mathrm{ne} $ might change with modifications installed at a later time (like an aerodynamic upgrade package). It would be nice, if the avionics would not need to be exchanged for this.


As to whether or not it is specific to Cessna: A quick Google search for "PA28 airspeed indicator" shows several Pipers with a lot of extra room (although some only have around 10 knots). I assume this is not much different for other aircraft manufacturers and just depends on which gauges where available.