Simplicity. For the # of social networks that people are into these days, the last thing they want is to have to manage 10 different apps across 5 different networks. Sure, if the network Im building gets huge and ends up with 100s of people using it more than facebook, maybe they'll want apps. But for projects that are just getting started, apps are overkill. Its easy enough for me to just hide the stuff with CSS, but that's a waste of processing power;)