Supercession is by definition the act of a media class to include, further classify, or incorporate into a more comprehensible form of media before the inclusion took place. A better definition by Gitelman and Pingree states that supercerssion is "the notion that each new medium "vanquishes or subsumes its predecessors."
Telegraph < Radio
Radio < Television
Beta < VHS < LaserDisc < DVD < HD-DVD/BLU-RAY < UHDV (Soon)
In this regard, each iteration of what we refer to as the medium we watch our movies on has taken from past generations of mediums, improved on the ideas and technological usage, and produced a format that 1-upped the previous generation in terms of quality, storage capacity, or cost.
Typewriter < Computer
Pc Hardware Every piece of equipment that makes up the common place computer undergoes changes monthly if not weekly to keep current. This process usually involves manufacturers attempting to push just a slight more speed or calculations per second out of a particular setup, building on what was done previously with the same hardware. When limits are reached the machinery is refined and a replacement is manufactured to better and faster specifications. Most often this is done at equal or slightly higher cost than the previous generation.
Supercession, Convergence, and Hybridization
Within the past few decades, different forms of media have come together to form what we have today. Through the convergence of multiple medias, hybrid mediums have developed which further the chain of supercession. This convergence of concepts suggest that, as a human race, we are constantly evolving our methods of communication through combining media and other such experiments. A good example of this would be an iPhone. They are essentially cell phones, yet they are made with the capabilities to store and display movies, music, and images. Not only does it come with unique media capabilities, but now people are able to hack them and customize them with third-party applications and tools. This shows how different media forms (i.e. video, music, and images) can all find themselves embedded into a single phone, purchasable by the general public. The convergence of these media's have formed a completely new generation of devices.
Within the online entertainment realm, we've seen many forms of supercession, convergence, and hybridization. One (more than noteworthy) example is the emergence of Second Life. Much like many role playing games, the setting is based on various 3D environments in which the user can explore, interact, and socialize with other users. This "game" however, presents users the option of personifying or recreating themselves as they see fit, and expressing themselves in whichever ways their programming allows. This is the convergence of game culture, identity, and social networking. Further, Second Life is a marketplace, where the exchange of non-tangible goods for real currency is commonplace - adding yet another aspect to the equation:
Game Culture + Identity + Social Networking + Commerce.
With this in mind, the concept behind Second Life may be too large to be contained within the classification of a game, or a social network. It's something much different, and currently stands alone in all that it has to offer.