That is a fair point. Is this a situation where you asymmetrically powerful? I have to imagine you would have considerable clout to represent a fair bit of their revenue in order to dictate terms. When I wrote my comment it was in the vein of a smaller organization.
I am but a technical cog in the machine my friend, while I know about what goes on in business and contract negoatiations I cannot comment on power dynamics. I would assume it's like any other negotiation - whomever has the greatest leverage has the power, I doubt it's ever fairly balanced.
Enterprise level SLAs are crafted by lawyers in negotiations behind the scenes and are not the same as what you see on random public services. Our customers have them with us, and we have them with our vendors. Contract negotiations take months at the $$$$ level.