grither, as you describe it, your concept of a possible "pre-arranged" settlement doesn't make sense from a negotiating stance. If Interdigital believes they are due revenues based on the existing contract, they would have no reason to concede on future rates based on present expectations.
However, the best idea that I've heard put forth was that Nokia may have wanted a reduced rate or capitation of fees (a maximum expense per year based on sales, etc). This to me seems more plausible.
But the point of arbitration would be worthless for Interdigital if a structured agreement existed like you suggest. Matter of fact, IMO, if the parties were able to agree to that, we would already have a settlement and wouldn't be waiting for the award to be handed down.