Ok. Lets break this down a bit what we are talking about here is if riot should implement price discrimination (particularly group price discrimination). While it's really not our decision, lets talk about it anyways (because what else is reddit for).
Ignoring possible legal issues that could come up from price discrimination (I don't think their are any in this case but considering this would involve EU law, US aw, Canadian law, etc. Who really knows for sure?) it has a few problems and benefits. Lets start with the benefits.
Firstly it would allow Riot to gain more profit by tapping into lower income markets. Which is good for them. (however if you look at wealth distribution the amount of money they stand to gain is "minimal"
Secondly, it would allow the poorer sections of the world to enjoy content they otherwise never would be able to enjoy. This will bring a great deal of good will for the company.
That's about it for the good things, but here are some of the possible bad things that could happen.
Gaming the system. How can Riot know for sure if someone is from say Macedonia if they also play on the EU server? IP address could be faked easily. They could request proof of citizenship but that would seem invasive. With different prices for different regions of the world you would also have to worry about people selling accounts with skins for less then buying those skins would cost in other locations. It also causes large questions. If John is from BR, has a BR account and is now going to school in the US, can he move his account to NA? He got skins for a lot cheaper than anyone else on NA should he be allowed to do that? How about people that want to level up BR accounts, buy cheap skins and then move those account to NA to sell them?
Next up, a major part of the value of a skin is in it's exclusivity, by selling it for cheaper, or longer than intended, you diminish the value of that skin (some people might find that stupid, but it is how it works). Is it ok to potentially diminish the value of other people skins by selling them for cheap to people that can't afford it?
Lastly you have address the issue of is it fair to actually charge some people more because of where they live? (as apposed to relative to minimum wage).
Honestly at the end of the day neither option is fair (ethical is a toss up) but that's because we don't live in a fair world. Some places are poorer, some places are richer. From Riots perspective, trying to keep RP an equal cost all round and charging the same price to everyone is simply the "best". This addresses the reselling of skins (as it's no cheaper), it also means people in the the wealthy regions don't feel screwed over and considering they probably would probably make up 80+% of riots income who can blame them? This also means Riot can let people change regions while not worrying about have to ask questions like "should this player be allowed to use their skins on the new server?", "should this player be charged an additional import/tariff on their account because of the skins?". Lastly this preserves the "integrity" of the skins that are out their because the remain at an equal level of exclusivity internationally.
TL;DR should Riot start using price discrimination? Financially maybe, Logically no, Ethically up in the air (a case could be made either way based of most of the fundamental ethical theories out their)