[Why Global Master Page Elements on Individual Pages?]

That's something I'm also curious about especially because it would make many things easier if you could fill picture frames individually for each page.

[Master Pages and Picture Frames]

As somebody who designs a lot of photo zines, a feature I would request is the ability to create a picture frame in my masterpage with the desired size etc. and fill it individually for each page that is based on this master page.

This would make a huge difference when designing picture-heavy stuff like I do most of the time! Even though Publisher is already a very good program and very easy to use.