Anything that adds heat inside the chassis has a cost in performance, not just heat (and the result of the fan running louder).
Putting a power supply inside of the Mini adds another component, crowding an already crowded interior. The additional heat (and most likely another dedicated fan) will also crowd out something. The result? Most likely performance cutting measures inside the box. We all want something outside of an on-board video chip. Well guess what? Even though the chance seems remote that we'll get one, it will be reduced to absolutely zero chance if they put the power supply inside of the Mini. I'd rather Apple do a number of other things (like include a separate video processor, or redesign the box to be friendly to opening so we can add RAM and/or swap out the HD, or add an HDMI output) than include the power supply inside.
Putting a power supply inside of the Mini adds another component, crowding an already crowded interior. The additional heat (and most likely another dedicated fan) will also crowd out something. The result? Most likely performance cutting measures inside the box. We all want something outside of an on-board video chip. Well guess what? Even though the chance seems remote that we'll get one, it will be reduced to absolutely zero chance if they put the power supply inside of the Mini. I'd rather Apple do a number of other things (like include a separate video processor, or redesign the box to be friendly to opening so we can add RAM and/or swap out the HD, or add an HDMI output) than include the power supply inside.