The above model is a very generic core for all diffusion processes. Consider new product sales (sales.mdl):
adoptions has become sales, and if you recall the behavior of adoptions, this means that they are small for a long time, then they explode, and immediately collapse. Many companies, such as Atari, have gone through this. Even though the process is generic, they surprised everyone (especially themselves) when their amazing success went bad.
Or consider the spread of a disease (flu.mdl)
Both of these are exactly the same model, with just the names changed, and both make sense. In order to elaborate either of these you might want to make different changes - adding distinctions between symptomatic, asymptomatic, contagious and non-contagious flu victims, for example. But even as you add structure you will find that strong parallels often remain.
