Morrowind: GCD (Galsiah's Character Development)

Oblivion: nGCD (not Galsiah's Character Development)
You would like this:
https://www.youtube.com/watch?v=aSy9GLi2H44

Sometimes, I like it when abilities determine their power in unusual ways. For example:

* In Final Fantasy 5, Blue Magic has interesting properties. For example, White Wind heals the party by an amount equal to the caster's current HP; Goblin Punch is like a physical attack power (but using the listed attack of your weapon and ignoring any special properties it might have (like that one weapon that only does 1 damage despite having high attack power)), but does 8x damage if the caster and target are the same level; Blood Suck which does half the difference between the caster's current and max HP, healing the caster by the damage dealt; and many others.

* A smartphone game called DotQuest EN has a dagger skill that heals your party using the character's physical attack power instead of intelligence.

* SaGa 1 and 2 have weapons that use magic power to determine physical damage, as well as weapons that do fixed damage, ignoring stats.

I find it interesting when games have mechanics like these.

Here's a better link for GCD: http://mw.modhistory.com/download-55-6955

Two reasons. First one is balance. If one stat governs how hard you with in both melee and range, that is the one stat that everyone will want, with dexterity being reduced to a defensive or dump stat. Second one is that hitting a moving target is not a strength requirement, but a dexterity one. So the dexterity is used as a gauge of how well you can hit what you are aiming at, though you may not be able to damage it.
And there are bows in RPGs that also have a strength requirement to be able to draw them. Whether they get a damage bonus or not from having a higher strength than the minimum requirement differs from system to system.
Specific skill increases lead to level up. You can make it so you won't be able to level up at all (I think so at least, mostly due to armor and weapon restrictions), though you can continue raising the rest of your skills without issues. Not entirely decoupled, but I wouldn't exactly call them coupled either.
Sometimes it can be fun, other times not so. Back to the "well implemented" I was talking about.

Yeah, I agree. I think besides making money with auction houses and the like, it's also an easier way to create challenges in the game with less effort. By rights in RPG-like settings, there should be different monsters over a variety of locales (where they can be partly randomized like in Diablo 2 and/or level-scaled too).

While it wouldn't be impossible to defeat them (including bosses), different classes + corresponding skill sets would either have an easier or harder time facing each type of enemy. This provides replay value and encourages the player to experiment with many skills/classes to see all their outcomes. However, such will probably require a lot of work on the programming front.

So, I guess effort vs result?