Melancholy Melanoma
It's not unfair, like I said, in reality you're saying "because I can't afford cash, but someone else can, it's not fair that they can get 100% rate." Yes it is fair, because they can afford it.
It's actually completely unfair because wealth in real life is not distributed fairly and an unfair advantage of wealth also translates into an unfair advantage in the game.
That's okay though. It only becomes a problem if poor player A feels that the amount of entertainment gained by rich person B spending cash (in the form of the game rewards being better/easier to acquire and thus the game itself being more enjoyable) is greater than the value of the cash player B spent.
So yes, saying it's not fair that players who spend money to advance have an advantage is justified. It's subjective, though, and there's a very fine line to walk between being "fair" to people who can't pay money (who want to play the game and have fun anyway) vs those who can (who expect a certain amount of value for their cash).
Personally I think that catch rates could stand to be tweaked a bit in both directions. It's too easy to catch beginner stuff, which often has a 50% catch rate without actually damaging it, and too hard to catch rare stuff, which can be below 20% even when they're dying. A small adjustment to tighten the overall range would probably make everyone happy.