Why this apparent obsession with pony avatars?

I’ve been loitering on some forums other than Fluther, and an incredible amount of people have brightly colored cartoon ponies with huge eyes for their avatar. It’s extremely irritating. Is this just some meme that’s blowing through? Has it been sparked by a popular Youtube video? I must know, I just don’t understand the logic behind it… I haven’t seen it on Fluther, though.

Example: http://www.minecraftforum.net/topic/490863-wtf-is-the-nether/

There are at least three avatars like this on the first page alone!