Its TNT! They're jacking up prices so that people have to resort to buying Neopoints with real money.. and TNT owns all of the real world item trader websites!
lol at this post. Anyways, scores sent 8x a day resulted in more pure neopoints in the hands of the neopians. The more money that people have, the more they will spend. More codestones were being bought then put back into shops for low prices, thus they became inflated in price.
Heres an example. Bob used to make 9k from games everyday, buying one codestone a day. Along comes april 2010 and 8 scores allowed per day, now Bob can make 24k from games every day. That is 2.66 times more NP then before. Now Bob can safely buy 2 or even 3 codestone to train his pet everyday while still having NP left over to save up.
Multiple Bob by the number of neopians that buy codestones, and you have a ton of codestones being baught with a smaller ammount being braught into the market( from Keyquest and RE)
As the lower priced codestones get baught out, the prices gradually increase, and that increase is outpacing the new codestones entering the market at low prices.
If this doesn't clarify it for you, I really don't know what will.