I suspect this has more to do with the estimated 200% price increase that Fox is charging Shaw and all providers. If only 1/3 opt in, no increase in cost to Shaw.
I suspect that this is also a message to Canwest. Don't try this method in order to get out of your financial mess. Shaw will "optin" channels like Tropolis (which I wouldn't pay 2 cents for). Canwest would lose on both subscription payment and ad rates.