We can lay the blame for this one squarely upon Billboard magazine. Once upon a time, they had a chart called "Race Music", which was renamed "R&B" - Rhythm And Blues. As this chart came to be dominated by other forms (funk, soul, disco), sometime in the 1970s it was renamed "Black Music", and so it remained until 1990, when Billboard decided it wasn't really on to keep using the name and reverted back to "R&B", presumably because the music featured had, if you really stretched the point, some sort of ancestral connection to what we know as Rhythm And Blues. And so the music featured in that chart - anyone remember the term "swingbeat"? -became labelled "R&B", the term crossed the Atlantic courtesy of record company publicity departments, and there we have it - a new definition for an old term.