No one pays publishers anything, unless one of the platform holders is cutting an exclusive deal. They simply earn revenue off sales.
Sure, launch titles have to deal with smaller sales, usually - although some can emerge as blockbusters and sell millions beyond launch, ala Halo or Mario 64 - but it's more about supporting a system with an eye on the longer term, I think.
That said, though, do platform holders reduce royalty/licence fees for launch titles? I'm not sure. But I kind of doubt it.