There is a work around for Newstand to be added to a folder like with all the other apps:
First, take two apps and create a folder. Second, as soon as the apps are in the folder, drag Newsstand into the folder too. As long as you’re quick enough, Newsstand will go into the folder!
This next step is vital as if you dont follow this step then you will crash Newsstand:
If you open Newsstand while it’s in a folder your springboard will crash. If you want to use Newsstand at some point just take it out of the folder and you’re good to go!