As a general rule commuter bikes are supplied with the most basic shocks. These are usually single tube Emulsion type shocks (The Oil and Nitrogen gas are mixed in the shock). These shocks generally have a spring preload adjustment and may also have a rebound adjustment screw at the base of the shock.
These shocks can work fine for general use on good road surfaces, but become more challenged when pushed. They are also fitted with a standard Spring which may or may not suit your geared up weight and usage.
A Custom built aftermarket shock such as Wilbers will be sprung to suit the riders weigh and will also be fully rebuildable. (Shock oil breaks down over time and looses its damping ability). Aftermarket shocks are available with different levels of adjustability. The most basic ones (Ecoline Shocks) are sprung to suit your weight and are fully adjustable for spring preload. An intermediate shock such as the Wilbers 640 is Custom sprung and adjustable for both spring preload and rebound damping. You can choose one of these options for your road bike depending on your budget and riding requirements. Both options will be a big improvement on the average stock motorcycle shock.
Sports bikes and Offroad bikes are usually fitted with a fully adjustable shock by the manufacturers. They also have a Nitrogen gas reservoir (This may be mounted directly on the shock or connected by a hydraulic hose) This reservoir keeps the oil and gas separate in the shock. This gas is usually at a pressure of about 150 psi and helps to stop cavitation or foaming in the shocks hydraulic oil. (cavitation would cause the damping to be less consistent)
These shocks just like their more basic brothers are fitted with a randomly selected shock Spring. This may or may not suit your weight and usage. They have a rebound adjustment screw and a compression adjust screw. These adjustment screws when turned may or may not make a noticeable difference to the shocks damping. It depend on many things from the size of the valve seat to the shape and angle of the adjustment needle. These shocks can also be quite good on A roads but also show their limitations when the pace quickens and where the road quality deteriorates.
There is a reason why track bikes are generally fitted with fully adjustable Aftermarket shocks. These Shocks are sprung and valved for the riders weight and usage (Road, Road and Track, Track use only). The shocks are adjustable for Spring Preload (Using manual preload collars or a Hydraulic Preload Adjuster with a control knob).
Rebound damping (Usually a screw or thumb wheel at the base of the shock) and both High and Low Speed Compression. (these adjusters are generally fitted to the Nitrogen Reservoir) There may also be the option of a ride height adjuster (This is useful when making geometry changes to the motorcycle).
Most racers with have their Shocks rebuilt once or twice a season. The damping is provided by shim Stacks within the Shocks which are fine tuned to suit their intended purpose. I would recommend fitting one for both spirited riding and all race use.