It is most certainly both. If the only factor was the virility of 4chan, things like the Nicholas Cage "Ya Don't Say" face would be the only things on the Internet, but that clearly isn't the case. Ponies appeal to human nature in a very unique way so as to inspire thoughts of humility, kindness, open-mindedness, and acceptance towards your fellow human beings. This is the unspoken, albeit perceived, message which draws people to ponies, I think.