Your personal experience seems to be with 720p converted from 1080i by your stb (which is not the best conversion medium anyways) as you already said. Better start making a few personal experiences with real 720p...
And yes it makes a huge difference not only in sports, but also in movies with special effects....
Technically speaking, in 1080i though scan lines are higher, only half of the pixels are used at a time, to give an optical illusion that resolution is higher. In most cases it looks almost like 720p, or even better in rare cases where pictures have hardly any movement... But then, none of these picture splitting algorithms(Adams are mostly used) are perfect, and they start making mistakes, resulting in a few broken images. Yes, some people may not notice, but most do, especially videophiles like me...
And lastly, I'm not quoting any random blog, if that was the cse, I won't be so passionate about it.
Since I'm having a specialization in compute graphics in masters, I feel its my duty to correct people with misconceptions regarding the subject... I feel I've tried hard enough to explain, but if you're still in denial, I can't help it. Maybe if we personally meet someday, I'll be able to explain and demonstrate you with the most minute details.....
