I agree that rubber matting would be essential if horses are just housed on concrete.
But w the wood floors it isn't needed IMO.....its soft enough to be comfortable for thier joints etc, and durable enough to withstand horses urine. Again this is w proper cleaning. I don't bed our stalls exceptionally deep...just ensure they are thoroughly cleaned
I personally hate rubber matting, as moisture can get trapped between the floor and rubber matting causing more damage to the flooring. But of course this is just my experience and opinion. Everyone will have their "favorite" combination.