not all, but most smashes tend to be very sparse/simplistic with their production and usually only involves like a bass or two, with a piano note and an acoustic leading everything else.

prominent examples would be Irreplaceable, Diamonds, Somebody that I Used To Know, We Belong Together, Love Story etc.

why does radio really seem to catch on with organic-sounding pop songs?

EDIT: all of Adele's smashes.