I don't see the contradiction "paying partners to secure browser placement" =/ "exclusivity." This just means you can have partner deals, but that they can't be exclusive, right?
Google can afford to pay more per user/click because of scale economies; their cost per user/click is lower. So, great, Google will pay Apple $20/user/year on a nonexclusive basis, and Firefox or whoever are free to match or exceed that, so long as they don't mind losing money on every user.
Are you saying that 'til now, Apple/Firefox _only_ took money for search default from Google due to the wording of the contract? In future, all the search vendors can pay all the browser makers for a position on a list of defaults?