If this is the case, and I can see how it could be, it really should be a story on CNet or somewhere.
Hey media folks, have a look at this story...
I just added this to my post above but will say again.
On Sky boxes, catchup content via ITV, C4, and C5 is downloaded ad-free to the box. This makes me think Sky have a deal with these networks to provide their content, and must be paying them something for that. However, I think it means Sky has some influence and I wouldn’t be surprised if some clause in the contract prevents the networks from launching on Apple (it may not explicitly say this, but it will be implicit) - some sort of “exclusivity” crap.
I would say it’s highly likely the reason ITV, 4 and 5 are not on Apple TV is legal and I’d put money on Sky being behind it all (or something like Sky).