Humayun, my apologies if I made it sound like you referenced Christian Buil's article.
Your points still stand and I agree with all of them but what I tried to say is that one of the possible reasons people use mainly Canon in the forums is that until recently there was no real competition in the field of astrophotography (AP). Nikon was based on CCD technology which was not as good as CMOS for AP, but things changed.
Now I am not trying to say that Nikon is better nowadays but the technology changed a lot recently and old comparisons are useless. I have seen some excellent results for D40 but could not find no direct comparisons for newer Nikon models. Just people's experiences which range from great to bad.
This guy even praised D50 over comparable Canons (at the time of writing).
However, any conclusions based on subjective tests are useless if you ask me. I would like to see more tests like Christian Buil's articles and until then I agree (as I already posted above) that Canon is a better choice.