The conversation would go something like this:
AFL - "we would like you to give Fox Footy a HD feed of your matches"
Seven - "Is it in the contract?"
AFL - "No"
Seven - "Well take your 1billion dollars and shut up"
God knows why it wasn't in the broadcast terms that every game had to be produced in HD and made available. I would guess that there would be a term that if Seven broadcasts a match in HD they would have to provide Fox Footy a HD feed by I'm only guessing. Could be a long 5 years.
(Assuming I can add!)