You seem to asume that everybody plays origin-chars just cause they already have
all the story maybe more than you can create yourself with a custom one.
I would advise you to look at this poll made by Larian which sees things a "bit" differently. Granted Beast and Fane were not yet avaible at the time the poll was made, but still it shows that people are interested in origins-chars but thats not their major focus at all.
http://www.strawpoll.me/11084333/rI don't think he's saying that everyone's gonna play the origin characters. I think what he's saying is the origin characters have a lot more going for them.
Imagine the difference between the party of one custom character who picks up the origin guys as companions, and one with 4 custom characters because people want to play a dude they make themselves. Everyone will have the same special power, there will be a ton of character quests and development that doesn't happen, and some things can't be resolved in a special way.
I've straight up told my buddies "If any of the special guys interests you, play them" because I'm worried that a group of all 4 custom characters will have a much less interesting run.
