Yes, I do agree with your points wholeheartedly. I got the white one as well, understanding that the teflon coating would keep it looking clean.
However, on a sticker on the box my phone came in is the following note:
"The back cover of your phone has been treated with a special coating to help keep it looking new and clean. Keep your phone dry to reduce the chances of dirt adhering to the finish. If the back of your phone gets dirty, remove the back cover in accordance with the instructions in the user manual and us a lightly dampened melamine foam eraser (aka. magic eraser) to remove any marks. After thoroughly drying the back cover, replace it on the phone."
(Their emphasis, not mine). This has nothing to do with the issue of your case causing staining (which I agree it should not do), I'm just passing along the information that came with my phone regarding cleaning it.