Yes Photoshop changes the way things work from time to time. In newer versions of Photoshop open documents are in a ring you can use next document forever and process around the ring.  In older versions of Photoshop open documents are just strung together in a chain. There is a beginning and an end to that chain.  In an action you need to know where you are in that chain and use next and previous to move around. With actions you need to be careful adding documents and removing document  for that will change the relative position between document. On the other hand Scripts will most likely be able to find the open document the want by name by running through chain.  Photoshop also changes its user interface from release to release adding and removing menu items.  When they remove item there is a good chance the some users action will break because the deleted menu item was inserted into the action and that stem will now generate an error message.

About the gray areas you stated you wanted to not have scroll bars.  You did not you still have vertical scroll bars. To get rid of these you need to zoom out more you will have more gray area. Also  Adobe keeps changing the frame around Image windows in cs2 cs3 cs4 and cs5 there is more information in the frames scroll bars are always there however they are grayed out when the zoom scale of the image completely fits within the window.  Here is what 4 8MP 3:2 Canon images look in CS5 when you zoom out as far as needed.  In CS5 if you do not zoom out so the images fit within the windows only the active image window has active scroll bars however none of the image windows will contain the whole image like your windows with the scroll bars.

I could show less gray if I could somehow record or insert something into the action to scale my 8MP images to 21.5% but I can not find a way. I also do not think a script can do that either.  Not all Photoshop function is scriptible.  I did not see anyting in the scripting guide about scaling or zooming a Photoshop image window.  When you can not do something using Photoshop script programming you can often use the Action Manager interface. The ScriptListener plug-in can record anything that Photoshop can record in javascript and vbs code.  In this case the ScriptListener would not help for things the action does was not done by recording Photoshop steps instead Photoshop menu Items were inserted into the action.  So in this case a script may have to resort to playing an Action to zoom and tile image windows.   If I could zoom all windows to 21.5% the view woul look like this

Your images would show more gray because of their aspect ratio. While my displays aspect ratio is 4:3 if  you subtract the Windows Task Bar and Photoshop bars areas from the 4:3 displays area the areas left in the Photoshop Window for its images windows is a close match to my 3:2 Images. Your images look like they have a 5:4 aspect ratio.