BI have addressed this in the past. First off, what most people fail to understand is that ARMA is not intended to be a full military sim with ALL the bells and whistles; otherwise they wouldn't make VBS. If I remember correctly, VBS already has an intricate wounding system, and if they wanted to include it in ARMA 3, they would have already.
The folks at BI have said that they want vanilla ARMA to be accessible, and that including really hardcore features like right off the bat might scare away more casual players (though I doubt there exists such a thing for a game like ARMA,) and hardcore players who wanted these features could download mods like ACE2.
Don't get me wrong: for me, playing without ACE is like ignoring the cake and eating the plastic platter the cake is sat on, but until they change their reasoning, expect stuff like ACE to fill the gap.