The only reason that media companies need fear cannibalizing app sales is that people have become accustomed to paying for Apps (even apps that are 99% content) but not paying for web sites.
Imagine for a second if Apple rolled out the ability to pay for anything on the web (that made it past a review process-- ha!) with your iTunes Store account?
Either Apple needs to extend their payment system out into the rest of the web, or the media companies need to band together hulu-like and establish their own payment system (or some micropayment startup needs to get some serious traction).
See also my previous comment on this topic: