I don’t know about any research directly supporting the distinction, but the two patterns you describe are intended to each be advantageous for different circumstances.
Dialogue Box Placement
Putting buttons on the bottom is a “dialogue box” design. It is best when you expect users to use one of the buttons and it’s the last thing the user does after making a single pass through the window from top to bottom. Often these buttons simultaneously execute a committing action and close the dialog, so they are necessarily the last controls used.
The bottom placement puts these buttons in easy sight and reach (e.g., when tabbing) when the user gets to the bottom of the form. They also cue the user that these are the last thing to do. Use this design for simple atomic sequential tasks where you expect users to go into the window, provide a couple values going from top to bottom, then select one button to complete the task.
Primary Window Placement
Putting buttons or other command controls along the top or left is a “primary window” design. It is best when you expect users to select multiple commands and they intersperse these commands with other input to your window (e.g., type a value, copy it, paste it elsewhere, edit it, save work so far, delete a couple items from a list, select a new item for the list).
Top/left placement makes these buttons among the first things users see when they open the window, giving them a quick way to identify the window’s purpose and the functions it supports. Use this design for complex multi-transaction tasks with multiple inputs and commands in various possible orders.
I’ve seen some apps put buttons along the bottom even when the window is clearly intended for complex tasks. I think this may be a hold-over from older style guides that stated buttons should always go on the bottom. These style guides did not anticipate complex tasks would be done in windows with buttons. Instead, they assumed complex tasks required a window with a menu bar, naturally located at the top.
One or the Other
I’ve seen other apps attempt to do both, either having buttons at the top and bottom, or a menu bar at the top plus buttons at the bottom. It sounds like a good compromise, but I would avoid it. Users may not able to guess whether a command should be at the top or bottom, leading them to sometimes search the wrong place. The Close button might be an exception since it’s clearly the last command a user can give in a window, but you may be able to achieve the same effect without the potential for confusion by having the button be the last control among those placed top/left.
