Broadcast hi def is 1080i with DD sound.
Anything can be broadcast in hi-def format, regardless of it’s format, but it’s not “upscaled” in any meaningful way. The most common example is movies. Most are DVD-quality being broadcast in 1080i format. While this does not improve the picture quality, it does make for a loss-less broadcast. Only content that is produced in hi-def is actually 1080i, unless a master is re-sampled at 1080i. AFAIK, this is not done.
The irony is that many movies and TV shows are now shot in hi-def video, then converted to film, then re-converted to DVD quality for distribution and broadcast. So there are perfectly good Hi-def masters lying around that are never seen.
If the mastering is high-quality, DVD quality (480p), can look very good on a hi-def monitor. But alas, most DVD’s are not “high-quality” due to compression using variable bitrate schemes and limitations of MPEG2.
If you have a true 1080i monitor, it’s not hard to see the difference between 1080i and 480p, although it might require a larger monitor if the 480p is especially high quality.