I could not disagree more. The content of the blues is about sadness, bad women(or men), love gone wrong, and other stories of depression; not marmalade in England. Also, the blues is a genre with its own form; that is why it sounds like the blues we all know and love. There is no copyright on chord progression, so you are not plagiarizing unless you are claiming St. Louis Blues to be yours, and besides St.Louis Blues is probably in public domain.

Sincerely,
Keith Gamble, Saxophonist