Previously capped at 20MB over 3G, iOS app downloads up to 50MB can now be downloaded over 3G in iOS 5.1. It's a welcome increase as devs aren't no longer handcuffed to a minuscule megabyte limit and have more freedom to do more stuff (if they want to hit that 'instant download' range).
The obvious reason for the increase is to not punish universal apps that have to accomodate assets for the new iPad's retina display. The apps are going to be ginormous, we already know that, so kicking up the app size limit will keep devs happy since users won't be warned to jump over to Wi-Fi to download their app.
This is good news! It was always sorta silly to have to hop onto Wi-Fi for a 22MB app. Downloading multiple 50MB apps is a quick way to hit your 3G data limit. Stick with Wi-Fi when you can still. [AppleInsider]