Well, when I play a character, I like to think that I should receive "advancement" from almost any action I take in the gameworld. I am playing a _game_, not punching a clock at my dayjob as a psychopathic adventurer. If I kill a foozle, yes, I've gained experience in that area, so I should get advancement.
It shouldn't matter, though, if I'm on a "quest" to kill the foozle or not. Why shouldn't I advance just because I've been tasked by an NPC with killing that foozle?
But by the same token, if I craft an item, I've gained experience (I know how to make stuff) and should receive advancement. Luckily, in this game I do get SP for that. However, if I run to a new zone, I've gained experience too (I know more about the world). I should receive advancement. Why don't I get any SP at all, either physical or class, for exploring?
Furthermore, if I were to complete a text-based quest, like reading what an NPC has to say, I'd have gained experience... I've learned more about the lore. I'm of the opinion I should receive advancement from that too! If that's too "radical," though, then combine that wall of text with a quest to kill ten foozles. Or make me walk to _that_ NPC and regurgitate what I've just been told, like taking a test. Did I actually _comprehend_ that wall of text? If I choose correctly, I receive advancement.
Instead, the _only_ way to advance in this game is to kill the same mobs thousands upon thousands of times. I can't imagine a world where that's (1) enjoyable for more than five minutes or (2) realistic. Certainly no "fantasy world" I dream about visiting has me get more powerful solely by wreaking havoc on creature. I'd go so far as to argue that grinding should _stop_ advancing a character. After you've killed your thousandth foozle, what experience did you really get from it? You surely didn't gain some extra insight into how to kill foozles, right? You didn't learn more about the lore of foozles. The foozles' blood is the same color for foozle #1000 as foozle #1.
So since _you_ get to continue advancing for being the biggest mass murderer of foozles since, well, since the previous player logged out, let me receive advancement for reading lore, exploring, and learning about the world.
Sorry this was so long-winded.