<p>the apps that demand you to invite all your friends end up getting more people (due to those invitations) than the apps that don’t demand you to invite all your friends. they confer selective advantage to the apps. Apps that are particularly invite-based, such as pirates or ninjas or zombies, get a huge advantage by means of this.</p>
<p>Well, if you looked at the Quiz applications that require you to invite 10 friends to see your results if basically trying to get more people so they change charge more for Ad space. </p>