glass, as much as i do agree with the logical construction of your refuting arguments, i must also point out that you use the same flaws which you point out. for example:
glass said:
is an <a href="http://www.don-lindsay-archive.org/skeptic/arguments.html#expert">Argument from Authority</a>.
----------------
an argument against the implementation of Armor as DR could start with the premise that "faster combat is more fun." this premisse is often found in the "tactical combat gets in the way of RP" camp.
---------------
consider the number of mathematical steps in using (pre-determined - your ac is alreay on your character sheet) Armor class vs. to-hit roll.
roll 1 d20. add pre-determined bonus
then if you meet or beat certain number, roll an arbitrary damage die (dice), and add pre-determined damage bonus.
subtract damage dealt from hit point total.
so, we have the possibility of 2+ rolls with 3 (possibly more depending on damage dice) arithmatic operations.
---------------
in order to add armor as DR, you create a greater variable scheme for situational modifiers (such as adamantine weapons bypassing DR) that must be constantly kept track of in combat.
you must also add an additional arithmatic operation (subtracting DR from damage dealt)
though it does not take much more time (and, depending on the players, possibly less time) to calculate thes additional operations, especially considering that there are no additional die rolls, it does add another layer of complexity to the equation of combat.
------------------
ok, now for an opinion.
as a DM and a player who is quite used to introducing people to the game, i find that adding that additional layer of complexity to what is already a complex and precariously balanced system seems unwise without totally re-writing the combat system.
------------------