In case you missed it: Last week, a Taiwanese gamer whose name translates as "Little Gray" finally "beat" World of Warcraft by earning every single achievement possible in the game. Not only is this a mind-blowing feat of dedication and an example of someone who completely lacks a life, it flies in the face of anyone who claims that Achievements - specifically those in WoW - are for "casual gamers."
It's true that the arrival of the Achievement system in WoW with Patch 3.0 (the preliminary patch to Wrath of the Lich King) coincided with a shift in design philosophy that made end-game content more accessible to players who weren't devoting their lives to the game. That's a simple fact, and I'm not here to debate whether it was a good thing or not - though I will say that I have to fight the urge to find people who complain about the game catering to casuals and slap them across the face with a sock full of quarters, because a business model where the majority of development resources are used on content for <10% of the player base falls just short of "completely idiotic".
Can you really claim that the Achievements themselves are for people who play the game more casually? On the one hand, it's true that the Achievements provide a nice little carrot on a stick for the players who can't find their way into the highest-end content. By providing a tiny psychological reward every time you hit the next multiple-of-ten level, loot X amount of gold, or defeat the final boss in a dungeon, it mimics the thrill that the top-tier raiders get when they down a difficult foe that they've been working on for three weeks.
For a player just starting WoW, they'll be earning Achievements from the moment they hit level 10, complete their fiftieth quest, or get an in-game pet or a guild tabard to show their colors. It's a series of road markers from the very beginning that provides another bar to steadily increase as well as gently nudging them in the right direction ("Oh, I just got my Scarlet Monastery achievement, looks like I should be going to Uldaman next.") In that respect, Achievements are absolutely meant to reward people who play WoW as a hobby and not a lifestyle.