Does a fighter player have to be an athlete and martial artist in real life? No.
Does a cleric or paladin player have to be a clergyman in real life? No.
Does a ranger player have to be able to track and hunt in real life? No.
Why does a wizard player have to have a high IQ in real life?
Why does a "face" character's player have to be a social butterfly in real life?
It seems silly to require a player to have the same traits as his character when the game is predicated on you pretending to be something other than what you are in real life. And it's even sillier when this restriction is only applied to particular character types, but not others.
Separate arguments, separate issues.
Again, changing wizard mechanics to be simpler won't change someone like S'mon from not wanting lazy or low IQ players to play high IQ studious character roleplay concepts, if his attitude is as I hypothesized it could be based on his statement.
His viewpoint could easily be the other way though, based solely on the mechanical complexity of the class. In that case simplifying the classes down to the point where all PCs would be comfortable with the complexity of the mechanics would fix the problem. However adding complexity to simpler classes like fighters would lead such a DM to say D&D is too complex for certain low-IQ or lazy players.
It could be a mix of the two viewpoints with him thinking that low IQ/lazy players should not play mechanically complicated or High IQ and studious roleplay concept characters and that a highly complex wizard class is a good match for the high IQ studious wizard roleplay archetype.
In any case I don't feel D&D design should be driven by reacting against such individual DM preferences but instead should drive to what will make the best game play for the most players. IMO that means varying complexity among classes to accomodate different player playstyles.
However the argument you pose in this post about physical in game described actions versus high IQ and talking character actions I consider a nonissue.
I am perfectly fine with having conclusions, decisions, and talking be handled fully by PCs.
These things can be handled mechanically through stats and rolls and DM direction, but I am fine with them being governed solely by PCs.
A Player need not know magic to play a wizard. I'm fine though with leaving players to make deductions on their own regardless of what their sheet says the character's intelligence is or how high they roll on a d20.
It is an arbitrary playstyle preference for which lines you draw between mechanics and player control. Same thing for what level of detail things are handled at.
In a LARP I would expect a character who wants to be a tracker to actually have their success at it be commensurate with their tracking skill and the situations they come across.
In a game where the player is not physically there to track this must be handled by mechanics.
In a game where roleplaying is handled by acting out your character you must be persuasive yourself to be successful at playing a persuasive character.
In one where roleplaying is handled mechanically you must either roll well or mechanically be good at persuading.
Drawing a line between describing physical things in the nonphysical story and the player's roleplaying out a 1st person interaction or making conclusions or deductions off of the described story seems a natural division to me.