I have 10,000+ static pages. Unless I employ an army of workers, I can't possibly move all of the whole site to Wordpress over the weekend.
Since the move involves fixing the whole taxonomy of the site, entailing changes in categories and URLs, I still want to do it section by section and not shock Google furthermore with URL changes of 10,000+ pages.
We were hit by Panda in Feb and got out in the summer - doing nothing. We just went on continuing to put out more content and developing direct and referral traffic