I played around with master pages on my ASP.NET 2.0 MCMS web site (see here for details on how to setup such a site).
My findings are that on a read-only website MCMS Placeholder controls work fine as well on the master page and on the content page. That's what I assumed when I wrote my earlier article.
Andrew mentioned that at TechEd the message was that placeholder controls in master pages will not be supported. So maybe there will be a limitation in web author that prevents this from working. We will see as soon as SP2 is available.