You'd better know what a flow is, otherwise have a look at the architecture document. In this particular case the discussion was started up by a statement by Van Jacobson who claimed that we should take care of rate limitation of aggregation generated bursts only in the service spec, since this is service specific issue. Rate limiters limit in the same way aggregation generated bursts and any other sequence of packets exceeding the configured maximum allowed rate. Paul strangely came up with a statement which you immediately and cluelessly supported, whereas Scott noticed that Paul was saying something inappropriate. That's why he made his statement.
Nothing called diffserv knows anything about per-flow anything.
A Chair of the Diffserv WG should now have sufficient elements to judge on Scott's statement. If you want further help call me at the phone number that you should be able to retrieve.