Well Drawmack, I can't say that I entirely agree with you on this one, but I do 75% or so.
I wouldn't say that training rules provide a way of quantifying realism (other than that, yes, they limit the variable), but a way of enforcing it. If the rule is there, the player is obliged to make the decision of whether or not to train; if it is not, anything goes. Rules can provide realism by enforcing it, by not leaving it up to the DM. If the realism of a rule can be circumvented then the problem isn't that no rule can provide anything more than a way of quantifying realism, but that some rules or poorly concieved or executed.
On the other hand, I do not believe that realism is entirely in the hands of the players and the DM. Armor makes you harder to hit rather than soaking damage and having to be repaired over time.
As per last week's rant, good and evil are presumed facts. If the meter for realism is the world we live in, the real world, that is automatically unrealistic, just like magic. However magic and an absolute good can be desirable things to have in a game.
For me, at least, armor that repels attacks, or the idea of using a system like hitpoints, then explaining it away with 'fighters are more adept at positioning themselves to minimize the impacts of attacks made against them' are not desirable.
So basically, yes, a freeform game can be very realistic; but, a game that uses counterintuitive rules can be guilty of enforcing a very unrealistic game too. Hence, you need, if not rules that enfoce realism, no rules that counteract it either.