Well, I'd rather go for too many than too few, and the trainers I listed are there for IC reasons. My reasoning is that if a mob looks able to teach a skill, then it should teach it.
I would think the most common grouse of the new trainer system is that spells/skills are located on 1-2 mobs, but these mobs are not the only IC-wise mobs that could teach them that.
An example, I'd be a bit pissed as a newbie if the place I'm levelling at (eg, Pleasure Planet) has many bartenders, yet I'd have to head to The Golf Course to learn drunk.
As for one zone having similar trainers, I myself feel that it would add to the atmosphere of the game, that the mobs are more 'realistic' than just a generic level x mob to kill. Though, I'm not sure if the [T] makes the difficulty of finding trainers harder, especially if mobs teach skills/spells ICly. I mean, a generic swordman in a zone is more likely to teach melee rather than cleave.
Oh..and I just thought of it. Bart should have word of recall, only because of his "I am new here", "Pay up, punk", "Darkness is forever", "In chaos is something" scripts.