title: What makes most programs need installation to run?
body: <p>I remember that "World of Warcraft" didn't require installation to run. You could copy the program's directory from the hard drive onto a different computer and run the executable. You could even run the executable from a USB flash drive on any windows computer you plug it into. This is obviously different from the gross majority of programs which require the installation program to run in order to work properly.</p>
  
  <p>How many reasons are there from software to require installation?</p>
  
  <p>What are they?</p>
  
  <p>Is there any reason why "World of Warcraft" was made differently? Why didn't it need to make any changes to the system registry, for example?</p>