Yikes. Didn't notice this was not available until you pointed it out. Ugh. This is heavily used at our site. Don't ask me why, they just do. Replace pics all the time. Worse, many do not grasp that delete+upload=replace.
Something else they do: once they figure out that their latest uploads display first, delete all their pics and upload again, starting with their least favourite. They love to control the order of their pics. Many ask outright "How can I control the order?".
No because it's the same image but improved.
I can only speak about my own case and the reasons why I need this feature. I run a community photoblog with a lot of emphasis in photo critique. It's very usual the members exchanging tips on how to improve each particular photo and is somewhat usual to see a photo going through 2 or 3 stages of changes based on the members feedback.