ChainsawAsh said:
Yeah, I guarantee the compression artifacts you'll see from an HD broadcast will be worse than those on the DVD.

Actually, much of the time an HDTV broadcast down-converted to DVD will look better than the official DVD (but not every time...)

Obviously compression artefacts in the source depend on whether it's MPEG-2 or h.264 encoding, original transport stream or re-encoded to fit on a DVD9.

But you should also consider that many official DVD releases suffer from EE, DVNR or simply shit transfers (a la the old Blade Runner release).

However, the main reason for the improvement is that DVDs are targeted to the lowest common denominator - those with interlaced CRT displays. Thus, the image on a DVD is usually filtered vertically to reduce the effect of "interline twitter" on these screens. An HDTV transfer will more often than not end up having more vertical detail.