Nihilism, a self-defined belief of nothing (and, in a sense, everything), tells us that there is no absolute truth, inherent value, or meaning, in anything. In other words, there is no difference between the pious man and the sinner because there is no objective standard to determine which to be better (and when I say "better," I mean on ANY good/bad scale, since nihilism would reject all the scales anyway).
The end to following nihilism, according to Nietszche (and according to his own brand of the philosophy, which he would never refer to as such), was to find an equal love (and, in some ways, an equal hate) for all things in the universe. From puppy dogs to genocide, it's all the same. The result is a sort of anti-authoritarian stoicism.
Emo, on the other hand (though the word has really LOST its meaning over the years), derives from the word "emotion." The early emo music scene was hailed in the mid 90s from those who were so benumbed by culture, but found themselves able to "feel" emotion with these songs.
Here's the difference between nihilism and emo, using the red dragon Drakengard quote.
"What's the difference between a man who prays and a man who kills?"
Nihilist's response: "nothing. Exactly my point."
Emokid's response: "probably nothing. And that makes me sad. *slashes wrists*"
The clear difference is that "emo" denotes an unending melancholy and teen angst. The quote in Drakengard has absolutely f**king nothing to do with these things, and if you think it does, that's because you are inferring it when you read it (making YOU the angsty teen). Anyone who's played Drakengard to its end knows that it appeals to the early-20th-century notions of nihilism and, in some sense, theatre of the absurd. Emokids may want to float around in this cultural realm, but that doesn't mean the two can be equated. OKAY?!
Final, semi-related point:
And... I'm tired of people using the word philosophical to refer to everything.
Too bad. In some sense, everything IS philosophical. Almost any given statement can have a connotation (or connotations) behind it, especially if you decide to put your own spin on it (as YOU did when you declared the statement "emo"). Check this: philosophy =/= depth. There are plenty of shallow philosophies and worldviews out there, such as materialism. And I dare say, the Drakengard quote is even more ripe for philosophical inquiry, considering it begs a rhetorical value judgment from the reader (that is, "which is better? IS there such a thing as 'better'?").