This is a strange one indeed. OneNote for Windows Phone 7 allows consumers to pin the create note tile to their Start screen, but this feature is amiss in Windows Phone 8.
That is unless you're using the latest hardware with the GDR2 update. We've checked on our Nokia Lumia 925 and it does indeed enable us to pin the tile to the Start screen, which has been confirmed by the OneNote team on Reddit.
An option to pin the new note tile is now listed in the main menu. We've not noticed anything else that's new, though we could easily be missing something else. Good news is the feature has returned and will be available when you update your Windows Phone 8 smartphones.