Something we may not always think about what our spells and abilities actually do in the setting of the game. Sure, for us, the tooltip tells us the basic information and we go on from there, but what are we actually doing? How does Arcane Shot work? Does the hunter just have a special magic arrow they shoot me with? Do they somehow wave the arrow around and it becomes magic, say a few words in Darnassian or Troll or whatever? Some abilities are pretty obviously spells, like almost everything a mage does, but for other classes the border between magic and skill can get pretty blurry... moves like Cloak of Shadows really beggar the imagination to explain in a non magical way.
A recent discussion on the forums about Thunder Clap and its being suppressed by silence effects (it always has, or at least has for so long that I've just accepted it) brings out Ghostcrawler to explain the reasoning. Quite frankly, it's a pretty reasonable explanation: if you're silenced, no one can hear the Thunder Clap going off, and thus, it doesn't do anything.