Why should umps have different strike zones?

I'm watching the Giants/Phillies game and already one of my big pet peeves in baseball has reared its ugly head.

Dan Iassogna, the home plate umpire, called ball four on Jimmy Rollins to drive in the lone run of the game so far. It looked knee high down the center of the plate.

An inning late, he called a pitch lower than the one thrown to Rollins a called third strike on Fontenot to end the second.

The boys on KNBR were talking about how Iassogna does not have a good reputation for calling balls and strikes.

Couple this with the Hunter Wendelstedt fiasco against the Twins and the general acceptance that certain umpires call high strikes but not low strikes... some call a ball off the plate... some squeeze pitchers... some don't...

Um, isn't that crazy?

Let's go to the Official Rules...
The Strike Zone is, and I quote:

...that area over home plate the upper limit of which is a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants, and the lower level is a line at the hollow beneath the knee cap. The Strike Zone shall be determined from the batter's stance as the batter is prepared to swing at a pitched ball.

Pretty cut and dry, isn't it?

And yet people just accept that the umpire will call it how they please.

You don't see this in other aspects of the game.
You don't hear "He calls the ball foul if it just falls one foot fair... that's just how he calls it."
Or "If you slide somewhere near home plate, that's good enough... that's how he calls it."

No. The rest of the game it is in black and white.

Now I am sure there will be many of the opponents of instant replay who will write in and say that one of the joys of baseball is seeing umpires take control of the game and decide what a strike zone is.

I ask "Why should a pitcher get squeezed and be forced to throw pitches down the heart of the plate?"

How about an answer to the question "Why should a pitch be a strike in one inning and a ball to another?"

And "Why should a 3 time batting champ get a favorable call? Isn't it hard enough to get a 3 time batting champ out without the ump bending the rules in his favor?"

I am going to make a video on this topic, but I would LOVE to hear a logical reason why the umpire shouldn't call a strike a strike and a ball a ball.