As of iOS 7, Apple changed how automatic downloads for Newsstand are triggered. Instead of enabling automatic downloads in its own respective section of the Settings app, like other iTunes in the Cloud content is treated, Newsstand publications now have the option to take advantage of background app refresh.
How to enable background app refresh for Newsstand publications
Launch the Settings app on your iPhone or iPad running iOS 7 or higher.
Tap on General.
Tap on Background App Refresh.
Find the name of the Newsstand publication that you'd like to automatically download new issues of.
Turn background app refresh to On.
That's all there is to it. Just enable background app refresh for publications you want to download automatically and leave it off for ones that you'd like to trigger yourself. It functions much the same as automatic downloads using iTunes in the Cloud, it's just in a different area.