The other point is whether having one consistent architecture and style maximizes usability. I don't agree that it does.

I'm inclined to think that it does. More importantly though in my experience, giving users an interface for publishing content that limits their 'creativity' (ie: the page layout is built for them, all styling is done through CSS, etc) means they spend more time getting the words right and less time on the fluff. Left to their own devices, people tend to come up with page layouts that are so hard to maintain that they become a barrier to actually publishing anything, or worse still the initial publish happens but the updates don't.