It has no palm support because you're not supposed to put your palm on it -- it's meant to be held by the thumb and pinkie at the sides (like the pilloried hockey-puck mouse).
If it was shaped to rest your palm on it, you wouldn't be able to use any of the multitouch features without fully removing your hand first.
And I think that may be part of the problem: I didn't find that to be a comfortable position to use the mouse even for short periods of time, having to hold my fingers and palm up and not having a resting, but still moving the mouse, position. I found it extremely hard to get fine control of positioning while clicking, I'd always end up moving the mouse slightly while clicking (incidentally, I have similar issues with the touchpad on the MacBook Pro).
If it was shaped to rest your palm on it, you wouldn't be able to use any of the multitouch features without fully removing your hand first.