Here's the tricky part: they do ask for permission to post on your behalf when you open the app. It's pretty muted, at the bottom of a popup, and dwarfed by a larger, more colorful call to action.

Here's a screenshot: http://i.imgur.com/oWDstiC.png

It's also not entirely obvious to me what happens in every case. If I close the popup, does it still count as my giving consent? If I close the app? My guess is that most people skim over the copy and click the big blue button, totally disregarding the checkbox down there.