Originally Posted by Scottnot

That's absurd!

Consider two DVDs of the same movie;

The first, a BD DVD which has been "well mastered" contains the movie at 1080p.

The second, a SD DVD which has been equally "well mastered" contains the movie at 480i.

Now, playing the SD DVD simply reproduces the entire content of the DVD, neither adding nor subtracting any information.

The content on the BD DVD, however, must be scaled from 1080p to 480i by the BD player in order to be displayed on the 1080i set.
It is unlikely that the scaler in the BD player will be as good as the mastering equipment that was used to manufacture the SD DVD, so it follows that the BD DVD on a "standard 480i set" may look worse; or it may look the same; but there is no reason why it can possibly look better than the "well mastered" SD DVD.