This is a big one. This is the big reason (imho) that the user base of the world wants an app for everything. But the web folks are slowly bringing the features of native apps to the web world.
Push notifications will be a big step in making web apps a more acceptable and pleasing solution for clients and users.
http://updates.html5rocks.com/2015/03/push-notificatons-on-the-open-web