• Classical economics [ E] distinguishes between two types of goods
• A good is substitutable if an alternative can be found by the user that meets their needs equally well and if the cost to switch is low or zero
• A non-substitutable good cannot easily be switched for another
  • infrastructure products (like network switches or operating systems) are inherently non-substitutable and benefit from network externalities
  • non-substitutable goods are more resistant to product life-cycles because adopting them involves a large cost
• Browsers are substitutable applications sitting on top of non-substitutable operating systems