Yes, thats it! Game over! That was exactly why I was asking the question, because I knew you were doing that method to compare!
Now let me explain it to you:
When you are viewing 720p by 'changing modes', you are not viewing 720p, you are watching the result of conversion from 1080i to 720p, as no Indian channel broadcasts 720p!
Now, without going into technical details, let me tell you, interlaced(i) and progressive(p) are two formats coded very differently, and converting from one to the other leads to massive loss of quality and detail due to incompatibility.
Since the source video is 1080i, 'changing modes' converts it to 720p, and the result is a diminished quality as stated above, giving you the wrong impression that 1080i is better than 720p. That was what I have been trying to explain you, and thats why I was stressing the question, as I knew where your misconception is...
Now, I request you to play a real 720p video on your tv, (one converted from 1080p will do), and compare it with 1080i. I assure you, all your doubts and misconceptions will be cleared..
And sorry if I was rude.....