I believe that's been upped to 100 MB as of iOS 7.The Twitter app might be not so big...
but I also got this for Pages, which is +200Mb, much bigger than the 50Mb which is normally allowed to be downloaded over cellular.
I tried to download an update yesterday which was well over 100mb and got the usual message about "this app is too large, please connect to wifi" but when I tapped the download icon again anyway, my iPhone just downloaded it without protest. This all happened over 4G I should add, wifi was off the whole time.
I'm hoping this becomes the norm in iOS 8, I've got 10gb that goes mostly unused.