let's say you wanted to buy a car, if you were to purchase all of the pieces it would cost more than it does to purchase an entire car. this is just an analogy, not a great one but it illustrates what is happening with micro-transactions. they take a game and break it up inorder to sell it for more than it should be worth.
lol has to be one of the most expensive games ever made if you want to purchase all of the content up to date.
http://euw.leagueoflegends.com/board...d.php?t=308717
this post breaks down how much it would have cost about 6 months ago to purchase every thing in the game.
in addition to just outrageous costs of the goods which they sell, their system they use is designed to separate you from your money. why should we have to buy RP in order to purchase something from riot? why doesn't it just cost money? because if you first have to buy RP you lose the sense of how much it is worth in terms of dollars. furthermore it leaves the bread crumbs of what you weren't able to spend, which increases the likely hood of additional RP purchases just to "clean-up" the RP you have left over (which is made possible by their not arbitrary pricing plan of making RP not purchasable in quantities that you can spend the entirety of).