I currently have two iPads (in transition), both running iThoughts and Editorial. One offers me Editorial, the other does not.
The 'not' offers texttastic and dropbox
The 'other' offers Textastic, Day One, Editorial, FTPpro on the go, Documents, Drafts, DropBox. All apps are on both iPads. I think Craig is about right here
I've never been able to figure out the logic of what is offered by what and to what