Does blizzard have stat-itis?

As a software developer there is one maxim that is adhered to by pretty much every software developer I have ever met: KISS - Keep it simple stupid

I am sure this term is well known for other fields of expertise but it most certainly holds true for any kind of software design. If your graphical user interface (GUI) isn't simple enough people won't use it even if it is the best program ever written.

If a user can't understand the application you wrote you might as well write it off.

I try to keep things simple when it comes to software and as a result it comes to me as a bit of surprise that there are so many stats in WoW that seem redundant or at the very least duplicate for melee vs caster.

Here's a few examples of what I mean:

Spell Hit and Melee Hit (or just hit of you prefer it)
Spell damage and attack power (not a 1 on 1 comparison)
Spell Crit and Melee crit
defense rating and defense

and pretty much every other stat that is split up into a 'rating' and a 'value' such as defense rating and just defense.

Not only are there a significant amount of stats the implementation seems to vary as well.

Taking a look at block rating and block value you'd think the relation would be similar to defense rating and defense but block rating in fact has nothing to do with block value.

But what is the point of having so many different stats? Does it add flexibility in terms of assigning item budget to items perhaps. It might aid designers in designing specific items for specific classes... but it also adds a high level of complexity to anyone picking up the game.

Why is there a split between a rating and a value? If x defense rating makes for y defense then what does defense add that isn't already added via defense rating? In fact any place where defense is used you could substitute defense rating quite easily.

By collapsing the rating and the actual value into a single stat (defense rating) you toss out a completely redundant stat without losing anything other than maybe a few smaller numbers on your character sheet.

This holds true for defense rating, but also for parry rating, resilience rating and all the other stats that have this ackward split between rating and non-rating.

The same seems to apply to crit and hit values. What is the difference between spell hit and melee hit? Well one is for melee and the other is for casters. But what difference would it make if you collapsed these stats into each other as well and just call it to-hit.

For spell casters it would still be spell-hit, for melee it would be melee hit but you no longer have 2 stats essentially doing the same job. The only real risk is that the to-hit for some classes would now apply to both spells and melee attacks but this is more of a balancing issue rather than a technical limitation.

By collapsing all these caster vs melee stats and getting rid of the somewhat strange split between rating and actual value you can compress stats. The result would be potentially easier item design. It is then up to the player to decide how to use this new itemization. If the warrior wants to don a cloth belt because it has a nice amount of crit on it then he can do so. This essentially means that all classes in the game will get a broader choice of items they can equip and the true limitation will be the type of armor you can actually wear.

Where are the technical and functional advantages to having all these extra stats? Am I missing a significant portion of information that seems to make these stats necessary or does blizzard have a bad case of stat-itis?