I agree with you here.
I could do a mod for you that would call your images from the server without calling image.php but then this wouldnt end up in future releases.
Im sure it would be simple for them to do this for the next upgrade 3.4.3.
Im supprised that its doing this at all anyway.
There is no point that I can see of calling a php file to then call a file when you could just as you say use <img src=$thumbpath.$imagefile>
