Here's the thing: The GPL combined with copyright assignments makes the dual-licensing business model possible. This is why we need to study carefully how this is done, and consider the consequences of assigning copyright.

(0) (the quote) is not in contradiction with (1) and (2). It is (1), a break from the situation implied in (0), that necessitates (2).

If all the contributors own their part and license it under the GPL, this ensures a level playing field. The GPL provides a shield for all involved. If they all assign copyright to a single entity, they lose their shield and this entity has the advantage. This is why that entity should provide something in return: a GPL-like guarantee.