It's a slightly more complicated than that.
This is probably the best, concise explanation you'll find online (
warning -
a tiny sprinkling of foul language, and one particularly raunchy remark at the end of the article):
The Herd Outsider's Guide to the Brony Phenomenon
I'm pretty sure I'm the only outspoken brony on CC, and that's fine. I'm not out to get anyone into the Herd. But when other people would post a cat picture or some other meme picture in response to a post (I love it whenever Duchess posts the "best friends" clip from
StepBrothers), I do so with a pony picture. En bee dee, yo.