Actually, Apple has a relationship with the Walt Disney Company[1], which owns the ABC, ESPN and the Disney channels - and many more. Perhaps these additional TV apps were added after enough content creators agreed to whatever terms.

Also, interestingly enough, there is a show on Disney Junior that first premiered on the Disney Junior iPhone/iPad app before it was shown on the regular Disney Junior TV channel. Maybe this is a new model to beta test new content?

[1] http://en.wikipedia.org/wiki/The_Walt_Disney_Company#Disney_...