The Crimson Binome
Hero
In many settings, money is hard to come by, unless you're born rich. Adventuring is one of the very few opportunities which is open to everyone, regardless of social class. Besides, the level 3 wizard who works for a wealthy merchant, and doesn't go on adventures, is not a PC. Regardless of how the setting works, the only characters eligible to be PCs are the ones who are fun to play, so it doesn't really matter how easily the NPCs can gain levels. (I mean, it matters in terms of having a setting that makes sense, but it's less important to gameplay.)I always wondered about trainer-blocked systems... why adventure at all? I mean you level and get better by training. So, why not do other things to make money then pay these tutors to get you your levels? Get a lucky score, marry well and go from pretty con man or lucky miner to 3rd level whatsit in the safety of walled splendor.
A similar problem shows up in any game where you can improve through training, without even mention of wealth. GURPS is the big offender here, because you gain 1 character point for every 40 hours (IIRC) of training, so it strongly incentivizes spending as much time as possible to train between adventures. If you can get away with only going on one adventure per year, and you can cram as much training into the intervening months as possible, then you gain something like 50 character points per year (compared to ~4 points per session, while you're actually risking your life on an adventure). The smart play would be to take seven years off at the start of the game, train until you're Batman, and then stomp all over the slackers who didn't spend all of their time training. It's kind of a problem.