Thanks, 57, for the bit of advice on how to really compare.
Technically, 720p contains abt 1 million pixels of information per frame and 1080i contains abt 2 million pixels of information per frame. So in theory, native 1080i ought to be better than native 720p.
Once a service provider starts upconverting and downconverting a broadcaster's original signal, who knows where you will end up.
Most US broadcasters, and all Canadian broadcasters, and some Canadian specialty channels, send their signals to distributors (satellite and cable providers) in 1080i. Ideally, everyone will pass through signals as is. Alas, that's not quite today's world.
Given all the above, it's not surprising that viewers able to capture CBC live OTA or a very well produced Blu-ray will notice better picture quality when their TV set is displaying 1080i/p vs 720p.