"1337" = "l33t" = "leet" = a bastardization of the word elite. Somewhere, at some point in the history of the World Wide Web, somebody thought it'd be cool to write using numb3rs 0r 0+h3r $ymb0|s in place of letters, it grew in popularity kinda like that All Your Base parody, and now every little kid who wants to pretend he's cool uses "l33tsp34k", even though the truth is it's just plain annoying.