I think the misunderstanding on DBeumont's part here is that he's taking the idea of decoherence in macroscopic objects to mean that they aren't governed fundamentally by QM when it just means we don't tend to see that kind of behaviour on our scale.

There have been experiments done with high numbers of coherent particles showing that it is a matter of maintaining the conditions to allow for coherence rather then some inherent exclusivity in macroscopic objects or that they are somehow exempt from the predictions of the theory, as you say, you can derive classical physics from QM.