It would not surprise me in the slightest if someone out there was pulling every post made on this forum or other popular bitcoin communities and trying every phrase or sentence in a brainwallet generator.

Even if not, the four quotes you gave are all compromised of a low number of English words. Even a brainwallet generator just randomly brute forcing combinations of English dictionary words would find them before long. I have no idea what the benchmarks for something like Brianflayer is, but as ranochigo points out, a single SHA256 function (and then the usual steps to go from private key to address) is not exactly resource intensive.