For example, AOL's, Primenet's, Tigerden's, NCF's and MCI's spam definition are tighter than the concensus ones. Indeed, some of these organizations have very large stables of lawyers. If MCI's lawyers say that they can act, believe me, they can. The ISP acts. The rest of us just act as a warning system.
Real laws are subject to interpretation.
If you try to be fair, moderately prompt and consistent, you will get few complaints. See, for example, the compliments that Jim Lippard's Primenet gets. You don't need universal arbitration. We're not having that much difficulty defining spam here. Not always true.