And yet...and yet...Tunesmith may well be partially right.
If the majority like it, it is popular, sure, but the chances are that is is not "at the edge", it "pushes no envelope", it breaks no barriers; ergo, it is middle-of-the-road. Not always perhaps, but very often. Examples:

Remember the popularity of songs like "Tie a yellow ribbon", "I never promised you a rose garden" - MoR. Hey, Britain is the country that elevated Mr Blobby to TotP, not to mention several other "novelty" songs; al MoR.

Even punk, or rock-and-roll were at their groundbreaking best BEFORE they became popular/fashionable, and before you could buy pre-torn jeans at the shops. You could argue that those tha followed in the genre were MoR for the category.

But not always; there is no 1-to-1 relationship here, and that's where the theory falls flat; but sure, it does work sometimes.