It's true that the constant stream of 6300 IP champs has made things challenging (particularly for those who either can't afford to spend money for IP and/or don't have the time to farm excessively due to work/school/etc). It's also true that making a champ at 3150 and another at 6300 cost the exact same amount in RP doesn't make much sense. However, I don't think Riot planned for people to try to get EVERY SINGLE CHAMP as soon as they came out. If anything, they want people to find a few that they like and work on perfecting their skill with them before moving on.
Think of it this way: you can work with the champs that you already have (and try out champs during free weeks), practice, become better players overall and be more selective about which champs you want to buy or you can just buy each new champ as they come out (whether or not you use IP or RP only changes the amount of work you have to do to get them), have less practice with the champs, and just have a ton of champs that you honestly are not going to use that often. Would you rather have 5-6 champs that you've mastered and regularly use or 30+ champs, where you only use about 5-6 and the rest are just wasted IP/RP?
Like I said, Riot could start sending out some lower priced champs every once in awhile. However, I see the reason (other than "Riot wants/needs to make money") why a majority of them are priced so high.