G5 and onward is where artificial skill comes in, eh? Interesting, only not really, as that tells me nothing.
Actually, it does give me a rough reference point.
(I need to learn to fish better.)
Say, how about that G5. Pretty neat how that thing does the thing, right? (Or is that too obvious.)
Well I'm not exactly allowed to teach it now am I?
Obviously Arthur has already given his analogy for it in other posts, but I'll try to elaborate on it to make it easier to understand exactly what he is talking about. If something on a tv screen (or the tv screen itself) is scaled up, and gets really big without a resolution increase, when you try to look closely at it, the pixels (each individual piece of information making up the whole) are scaled up too and are huge, so you're not really gaining any new details, it's the same amount information (i.e 1 pixel), therefore raw power only gets you so far. With a resolution increase, the space that used to be covered by one pixel is divided up into many more pixels, so you can see greater details and more pieces of information in a spot where you used to see only a single unit of information. Essentially, the size of your minimum unit of information gets smaller, so you can see the units that made up what used to be a single unit of information, therefore your precision and ability to work at higher levels of detail increases.
While this analogy is easy to understand in terms of senses, and it's not too hard to connect it to casting (if you think of a pixel as not only the smallest unit of information that you can see, but also the smallest unit that you can manipulate/control), I can think of another analogy that illustrates the effect and the benefit it has on casting. Imagine your hands get bigger. The muscles get bigger and therefore the hand gets stronger. However, when the hand gets REALLY big, despite huge amounts of strength, there are certain things that remain beyond your ability, because they require more than just raw strength.
As an arbitrary example, imagine a button that you wish to press. This button requires 5,000 lbs. of force to press, and is located deep inside a hole that is 2 millimeters wide. Your exceptionally large hands can easily exert enough force to press the button, but they are so big that they cannot fit inside such a small hole (keep the jokes to yourselves please

). So was your massive amount of strength enough to allow you to press the button?
Now imagine that you gain something that allows you to keep the same amount of strength in your hands that you had when they were huge, but makes them much smaller. Now you have the ability to wield the same strength with a much higher level of precision, and thus you can both exert the 5,000 lbs of force to press the button AND you have enough precision to get it in the hole. That's what a resolution increase does for casting.
[EDIT]: The hand analogy kind of makes it seem like adding power decreases resolution, but this isn't the case. Just clarifying, because analogies can get confusing if taken too literally.
Your anguish sustains me.
Madness is like gravity: all it takes is a little push!