Well let's think about it.
I tend to think that there is a fair amount of strategy involved in picking the right relief pitcher/pinch-hitter for a match up. Especially when you think of the game situation, defensive substitutions, players you have left in the bullpen/bench. I mean, it isn't rocket science, but it is one of the more strategic moments in any game. Think about it, what is the biggest impact that a manager can have on a game? I think it is clearly filling out the lineup card. He has to choose which players he wants going that day, and in what order, based on the matchup. With pinch-hitters involved, it basically gives the manager an opportunity to make an in-game adjustment to that lineup, most likely at a critical part of a game. That is an entire component that would be lost if you instituted the DH.
If its the 9th inning and you're winning, you bring in Marmol.
If its the 8th inning and you're winning, you bring in Wood.
If its the 7th inning and you're winning, you bring in your 7th inning man (currently Samardzija?)
BUT, if there is a tough lefty, or couple lefties, you bring in a LOOGY.
You basically rank the bullpen and bring them in, in order, saving Marmol for the 9th.
(I'm not saying I agree with this, this is just how managers manage)
If you're pinch hitting for your pitcher, you bring in an opposite handed bat of the pitcher, so you have a choice of 2 people; one will most likely have pop and one will most likely be speed/defense. Not a tough choice again.
Then with RP's up to bat, you ALWAYS pinch hit for them.
I just don't see any strategy here to make it more entertaining than watching 3 wasted at bats by the pitcher instead of 3 at bats by a real hitter. And it makes the job of pitching more difficult to boot. SP's are pretty much given 3 free outs...
"Don't worry getting that #8 guy, the pitcher is next"
Doesn't seem like a strategy that improves the game.