It looks like you're right, and that it's the classic case of two people arguing about the same thing. Here's a quote from the book linked to above

" ... In The Plan-as-You-Go Business Plan, Tim Berry makes these points much more eloquently than I ever could. Tim argues that the planning process (along with regular reviews) is so important that business owners just need to get started somewhere, anywhere, and continue to build your plan as your needs change. This is 180 degrees different from the classical "big bang" approach to business planning where we work for months at a time developing a huge document before we ever get started working on the business."