I can't believe that this thread is still going. Sigh........
I can't speak about other associations but in USA/ASA, if done right, before you become an umpire:
- You attend a weekly class over the winter for about 2 months where you study & learn the rule book.
- The class culminates in a multiple choice test that you must receive a passing grade on.
- You then receive field training where you learn positioning & proper mechanics.
There are also continuing education classes every year. There's a lot to learn & a lot to keep straight. During all of this you must also learn game management & how to properly comport yourself. You are only going to become competent over the course of time & experience. No 1st, 2nd, 3rd year ump is going to get everything right every single time & even the long-time vets are going to have a hiccup from time to time.
In addition to knowing a rule, you've got to know how to properly interpret & apply it. Reprimanding a fielder for simply moving on a pitch is most certainly not that!
Some rules are literal.
Some rules require interpretation.
In some situations rules must be combined with other rules in order to reach the proper ruling.
In some cases rules may conflict & one rule take precedence over the other.
Teams/Players are provided with a Rule Book. Umpires are provided with a Rule Book, an Umpire's Manual & optionally a Casebook & Umpire Clinic Guide. What this means is that if an umpire takes advantage of all of the resources available to them & is properly trained, they're going to have a deeper understanding than someone just reading the rule book.