Now that Pokemon Go has been out for a few weeks in the United States, some of the most dedicated fans are reaching the dreaded "level plateau", the point of the game where it's no longer easy to quickly level up. Around the time that you reach Level 20, Pokemon Go begins requiring massive amounts of XP (like 100,000 XP or more) to hit the next level. In addition, some fans are complaining that the game gets progressively harder at higher levels in a supposed attempt to force them to spend money on the game.
In a thread on the Pokemon Go subreddit (which is reaching toxic levels due to the game's many delays and Niantic Labs' perceived neglect of the Pokemon Go community), one user named /u/Riggnaros spoke about his experiences trying to reach Level 30 in the game. One particular complaint was that low level, common Pokemon seemed to run away much more frequently, which led to significantly more wasted PokeBalls. Riggnaros claimed this was a ploy by Pokemon Go to force high level players to spend money on the game, which is typical for many "free to play" games.
So, is Pokemon Go actually trying to "punish" players for reaching a high level? Well, yes and no. There's no question that Pokemon Go is set up to make it exponentially harder to level up once you reach a certain point in the game. That's probably because the game's designers don't want "hardcore gamers" who play Pokemon Go for hours at a time to have a disproportionate advantage over the more casual players who might only play on the weekends. Since the Level cap is only at Level 40 and there's only 151 Pokemon available to catch (146 if you take out the five Legendary/Mythical Pokemon that aren't available yet), Niantic doesn't want players to get burnout by "beating" the game after just a few weeks. However, there's nothing in the game data to suggest that low level Pokemon get harder to catch at higher levels.
Since Niantic has largely been silent since the game's release, we really don't know what their plan is for players who hit that level plateau and whether the game gets progressively harder. Pokemon Go will have a presentation later tonight at SDCC, so hopefully we'll get some answers then.