As it turns out... If I select Web Images Only option - DFP recreates the image as 72dpi but does not write the dpi info to the file - regardless of what the dpi of the original file is.
If I leave the Web Images Only option unselected then it leaves the original image alone and it retains it's original dpi and dpi data - however there is no width or height information available for the file.
Any thoughts on how I can get that width and height info when Web Images Only is not selected? Or how to prevent the image from being recreated at 72dpi and retaining the dpi info if I do select Web Images Only (which btw - IMAGES ONLY would be a better option).