Nah, I can buy the buyrate (hurrrr) being part of bonuses.
If we take one of the worst buyrates of last year, Night of Champions at allegedly 175k buys and multiply that by the $45 they want they that's $7.9million revenue. At the network announcement, they said that WWE only sees 40% of that, so we're down to $3.15m. If even only 10% of that is reflected in their bonuses, then that's $315,000 shared between at most, 20 guys at Elimination Chamber with the top of the card getting a bigger cut, which Punk would be part of. You're probably looking at a low end 5 figure sum for one main event match I reckon.
Even if my figures are off in terms of percentages and it goes to 5% of the buys split between the card for bonuses, you could easily extrapolate that for Wrestlemania which will do over 1 million buys @ $60 a pop, which according to Jerichos Undisputed book netted him a 6 figure sum against Triple H. But if the Network eats some of those buys and they haven't explained what that does to bonuses, that could be a big deal. Maybe Punk was only planning to stick around until Wrestlemania if we wasn't main eventing it anyway, take the cash and run, but now doesn't know how much he would get so he's just going to force WWE's hand to tell him how much he's likely to earn.