I think capitalism is fundamentally different than other systems because of one important nuance. In capitalism you can buy a plot of land and go start a communist society, or a socialist one, or whatever you want. So long as your little society can feed itself, you can do whatever you want. Well even if it can't feed itself, it can still do whatever it wants - but it probably won't be particularly long lived. But in socialist or communist societies you can't just go start up your own little capitalist society.