Agreed.
Although my preference is (as you stated earlier) 'graceful
degradation' in the face of congestion, not intentional degradation
of traffic based on some arbitrary monetray boundary.
Again, there should never be a case for _intentional_ "less-
than-best-effort", in the traditional sense.
Of course, these arguments assume that the service provider does
the Right Thing (tm) w.r.t. capacity planning & engineering. 
- ferg