For me, the joy of beating a game just isn't the same on iOS. Yeah, the story arc on "Angry Birds" is compelling and there honestly hasn't been more open and controversial ending than "Cut the Rope" but something about the whole journey just seems so abridged.
Yeh, iOS games arent exactly full of story, alot of the "RPG" games on there are very repetative, as its build for the gamer who doesnt spend any great deal of time at once playing so probably dont realise theres no story

. Ive played some good iOS games with good stories, by I only played them once or twice because you dont have time to get into the story.
For 3DS on the otherhand, you arent going to buy a dedicated console and not play on it. So the games have to have more substance.
Games over in the UK where I am are £30 GBP, which works out at more like $50 USD.