Update.--I spent the afternoon playing with the settings and preferences, and even some of the xml files, and nothing changes. I think the problem rests with the "Workspace" files which defines the workspace window size and position and the host of settings for each window type.
Well, it seems Dreamweaver CS6 (DW) is ignoring the opening settings. I tested this by copying the files from DW CS5/5.5 and nothing changes. These are the files which works with DW CS5/5.5. Anyway, I'll continue with DW CS5.5 for awhile because it works and wait for an update to CS6.
Ok, I have upgraded to Adobe Creative Suite 6 (CS6) Design and Web Premium with Dreamweaver (DW). I moved from GoLive (CS2/3) to DW CS4 then 5 and 5.5. And as usual with all new applications, you lose all the presets and preferences you had with the old version, and with DW this is the hardest part of this application, to reset to your preferences.
Specifically I keep all my DW windows, design and code, to the same workspace window size, 900 x 1024 (width x height) and when I start DW the windows always open to that size. This took awhile to set with DW 5/5.5 and now it's totally frustrating with CS6, and getting to be a reason to just skip DW6 and stay with DW 5/5.5.
This is because it always opens with a full screen view, like on a 2560x1440 monitor, really sucks to see your entire screen full of a window. I really hate this and haven't found the way to set the default window size when starting DW or opening new files. I want to throw DW out the window.
I still use GoLive along with BBEdit and Coda as Web page editors because they allow me to work with groups of files for the Website without having to close or reopen groups of pages. I can just keep them open or in the auto-open setting. And all of these applications remembers the default size of your workspace window.
Why can't DW CS6? With all the features and user tools and function, it can't remember a simple setting, like open all windows this size? Is that so hard to remember or have a user setting? Only you folks make it harder than it has to be, like almost impossible. So, if anyone there at Adobe or in the world at large can tell me how to do this, I'll be happy again.