It all stems from a desperate wish to participate.
I secretly suspect that most people posting answers to a different question entirely have, in fact, read and understood the question, but have nothing to contribute in response. In an effort to join the party, they post a tangential answer that addresses at least one of the keywords in the real question but ends up coming across as a total misread, thus making them look like thickos. Of course, some respondents genuinely are thickos, and are easy to spot as such.

QOTW is basically a way of honing one's skills as a raconteur. Some people are naturally good at it, and end up on the top page every week. Some people clearly have a story to tell, fighting to get out of what on the face of it is an insipid answer. Some people are just bored and will say any old thing in an attempt to get noticed.

If QOTW were a party, the raconteurs would be sitting in a leather armchair with a cigar and a glass of cognac, surrounded by a bevy of babes/studs (delete as appropriate) hanging on their every word. The 'fuckwits' would be wearing a comedy wig whilst leaning over an attractive guest, effectively pinning them to the wall, and shouting over the music about premium bonds or graphics accelerators.
( .Yeti. El amor en los tiempos del cólera, Fri 14 Oct 2011, 10:19, 2 replies)

Raises Cognac and toasts the post while blowing smoke rings.

( The Mock Turtle ™ --- Thinks you are a cunt, on, Fri 14 Oct 2011, 10:22, closed)

Hides in kitchen bitching about everyone else.
I
( scarpe We Stole Bikes, Fri 14 Oct 2011, 10:27, closed)

*shags your girlfriends while you both do so*

( Je suis un vagabond is an unfunny, up your own arse middle class knob, Fri 14 Oct 2011, 10:37, closed)

Eats a croissant
& sips some chardonnay.
(Misery McUglywife an attention seeking sociopathic fuckstain., Fri 14 Oct 2011, 10:39, closed)

I like this

(jennymnemonic, Fri 14 Oct 2011, 12:38, closed)