I think that Riot has been doing a good job with the champion rotations so far. They do not want to make the new champions free the first week of their existence because that would cut out a lot of buyers that like to play one champion a little and then move on. Frankly, I think this is not a bad business move. If you want to play the new champions right when they come out, just buy them. Also, if Riot were to make them free the first week, it would negate the new champion pricing (7300 IP the fist week).