Betcha someone else thinks up the name Ben
Another useless topic here goes...
I just knoooooooooow Obi-Wan isn't gonna think up that name himself.
Betcha sometime, somewhere, we will hear the words: 'Ths is my friend, Ben.'
It'll be some kind of scene where a friend of his is trying to sneak him in somewhere. A guard will come up to them and Obi-Wan's friend will say: 'This is my friend, Ben.'
Just my hunch cuz I can't see Obi-Wan sitting there picking a name out of there air for himself.
OR...if Luke is a toddler by Ep III he could mess up Obi-Wan's name cuz toddlers can't ever talk right.