I think it's more so to demonstrate that you can play a variety of characters. I think it's more on the lines of, "we already know you can win with those characters but what can you do with different characters."
That's the point. Without the ratio system probably it doesn't make sense choose other characters besides K', Raiden and Iori-Liz-Kyo-Kula. And well, videos of the tournament could be really out of interest and help people to get bored of this game. Of course, is something that it depens on players.
About Mature, I remember a vid with a very high skilled Mature player who played her without the infinite and he played very very well, showing that Mature is a dangerous and effective fighter. But she probably needs strategy, it's not like Kula or Liz.
Sad Romance's comment about Mature and Liz...