Really? The following paragraph is taken from the Astro website on FAQ for B.yond:

High-Definition TV programmes are currently being produced in 720p and 1080i, depending on which one the programmes producers decide is best for their show. We will be broadcasting Astro B.yond High-Definition channels in 1080i, which is in line with international industry standards.

What I understand from this is, even though some programs (eg, sports) may be produced in 720p, Astro would still broadcast its HD channels in 1080i.
So if you think you are getting better quality by setting your decoder to output in 720p for sports program, you may be mistaken. The sports channel broadcast is upscaled by Astro from 720p to 1080i, then downscaled by your decoder to 720p, then scaled again by your HDTV to 768 or 1080, depending on your HDTV.
What I prefer is to set the decoder at 1080i (same as Astro HD broadcast), then just let my HDTV do the scaling for me.

Just some thoughts on what I understand: correct me if I am wrong.