Dreamweaver required you to know quite a bit about HTML. Muse is like InDesign/Photoshop, which people use to do mockups of designs (not UIs/wireframes) today. It cuts translation to code from the workflow. That's a meaningful shortening of the feedback loop for a designer.

As for the rest of us, we don't have to be concerned till Muse starts learning the quirks and features of CSS faster than ourselves.