At times the line between "rock" and "blues" gets very thin. Early rock was blues-based, and one of the first recordings hawked under the name "rock" was "Shake, Rattle and Roll" which was a blues song done with a rockabilly -- that is to say, uptempo country swing -- beat.
Led Zep has done a LOT of folk/blues material, e.g. "The Lemon Song" which was a version of "Killing Floor," as well as a very nice rendition "Gallows Pole" with something of a twist ending.
But we all have our blind spots and thoughtless prejudices, don't we? Mine is against Rap, and I'm not a big fan of Heavy Opera either, although the comic stuff (G&S) I rather enjoy. I usually hate The Who, but "Squeezebox" is on my play list, cos it's so country/folky and fun.
Not sure why I said any of this. Anyhow, kudos to Kendall for being man enough to apologize.