You may say that, but at the end of the day, there are too many variables. The fact of the matter is that not all players are experts in close combat positioning... and even if they are, there WILL be situations where the enemy unit is just too darn close, the player made that one "opps" mistake, crappy Difficult terrain and Run rolls earlier in the turn, Impassable terrain funneled you too much, etc, etc... that'll cause their Xth model to come into contact with Difficult Terrain and thus force it for the entire unit.
At the end of the day, you just cannot drop an entire set of rules just because you're "Awesome" and you "obviously play a perfect game, with perfect dice rolls, every game"... only for the fact your opponent is not as Awesome as you are. And thus will blunder into DT. And thus both you and him will need to know these rules (otherwise he can con the hell outta your naive self).
Unless you're Batman. At which point I'll point out this is the 40k universe, you're actually Konrad Curze, and thus you belong to Chaos and should be purged...