There is a difference in how an army plays based on how skilled the players are in every game.
However, some games DO tend to have more ballanced game play due to having more tactical focus than 40k does,AND have a lots more playtesting than 40k recieves.
In 40k most units have a pre-defined purpose, (even the FOC describes pre concieved function!).
And as the game revolves mainly around inflicting physical damage ,with ranged weapons.Having no FOW mechanic to limit interaction , or morale damage to allow lower level interaction.(Supression etc.)
Means 40k is ill disposed to allow the sort of subtle balanceing other games allow.
Again I look at Epic Armageddon, and wonder why a more straightforward rule set with less complicated rules , and far more ballance, is relegated to the SG department.
EA is an example of how 40k could be if game play was the top priority of GW plc....