With the whole better Mobiles / iPad craze at the moment I think things are leaning towards closed systems as such.

 

Facebook, Apple App Store, Android Market to name but a few which have each proved highly successful.   

 

Interesting read along these lines; 

http://www.telegraph.co.uk/technology/internet/7954157/Ofcom-data-shows-how-technology-changes-our-web-habits.html