There are other products out there from Plugin Lab and others that let you update all the menus on your site with a click. I'm surprised Webassist publishing a product that is this far behind the others! 
I think there are two issues that can be determined from your original post a) getting the menu on to multiple pages and b) effecting changes to the menu.
You get the best out of dreamweaver by using templated pages so you add the menu to the template and then create the page from a template. When you make a change to the template it is automatically rolled out to every page that is created from that template. In otherwords change it once and change all the pages. No copy and paste to all your pages or any other such malarky. This isn't about the capabilities of CSS Menu Writer its about using the best workflow method provided by dreamweaver.
When the menu is on every page if you change it using the extensions controls then all copies of the menu are automatically updated.
regards
Jon
