Character growth and development in fiction is something that must come from more than mere combat prowess, but it is a common element of fiction that a character will grow more experienced at whatever they do over the course of the story, be it slaying goblins, baking bread or baking goblins. The thing is, their increasing expertise at this task usually has some ramifcations on the story. Harry Potter figures out how to summon a patronus and is able to repel the dementors, and Zoolander figures out how to turn left and is able to finally open a centre for kids who can't read good (and who wanna learn to do other stuff good too). In a good game like The Legend of Zelda: Majora's Mask (to pick a hugely underlooked installment), finding the hookshot allows you to do new things, and it appreciably changes the gameplay somewhat. In an ultra-conservative design like World of Warcraft, you will never find anything other than a sword or a helmet or a breastplate which gives you bigger numbers. Then you can travel to some strange new land with different scenery and fight enemies that have bigger numbers, but you'll be prepared because of your bigger numbers.
Now, to be fair, part of the difficulty here is with the open-world design of a game like World of Warcrack-*cough*-craft. Zelda, being a much more linear experience, is able to lay everything out so you find your hookshot at the right time, rather than finding it too soon and errently pwning a bunch of noobs who were minding their own business. WoW on the other hand involves gaining items and skills pretty much at random (at least as far as the developer's concerned), so very little plot or gameplay ends up being built around particular skills or items unless they are special McGuffin quest items. (On the whole, WoW is a very conservative game. Things like the Corrupted Blood incident illustrate how entertaining the game could be if the designers ever decided to start taking some risks. But I'll get back to the many reasons why I don't play WoW in a future post.)
Games that have even less of an excuse are single-player RPGs which may be as linear as Donkey Kong yet still refuse to confer anything to you that results in anything more than bigger numbers. Sure, as in WoW, there will occasionally be a semi-interesting ability which perhaps stuns an enemy or heals your party, which should change gameplay dynamics a bit, but you are likely to have something of every type fairly early on, at which point the game just starts jacking up the numbers. "You can already heal? Well now you can heal twice as much! You can already encase a party member in a protective field of energy? Well now you can do it for 1.3 times as long! Hooray!"
The worst of all this is that in many games, the abilities have no bearing on the story or the gameplay outside of the battles. Again, the problem is that the game may not know exactly when you will have gained a particular ability, but why in the bloody hell can't you cast cure or use a phoenix down on a wounded ally outside of combat? I'll tell you why. Because, in the words of Yahtzee, "the story and gameplay are kept either side of a rought-iron fence made of tigers."
Anyway, I don't mean to give the impression that I hate all RPGs (just most of them). I have no particular problem with numbers in games going up, just as long as I don't have to waste my time grinding through uninteresting battles in order to get my character to the level at which he can defeat the next boss. This is called filler, and it has long been one of the vilest scourges of the gaming industry. But rather than get totally derailed, let me get to the point of today's ravings: in-game purchases are a load of bull. You shouldn't have to waste valuable time or money just to get big enough numbers to play a game properly. It's like if you went out to have a good game of tennis, only to discovered that your opponent had bribed the judges into letting him use a Maxim gun instead of a racket. That may be a poor example, though, because it would appreciably change the gameplay.
The only ethical way I can see of doing paid content is if it actually opens up new parts of the game to you. Paying to download new levels or areas seems fine, as you are getting more of the game. Paying real money for a digital sword that does x2 damage goes against everything that I stand for.