We can apparently blame the Interwebs for the OED's mass killing. "People are not confident about using hyphens anymore, they're not really sure what they are for." And: "The hyphen is seen as messy looking and old-fashioned." There's always been a tendency for two words to "date" -- the hyphen as chaperone -- and then marry, becoming one word. But interesting to me are the words that have "broken up": water-bed is now water bed, and ice-cream is now ice cream.
And it's true, they do seem old-fashioned (oldfashioned? old fashioned?). Consider the Onion headline from 100 years ago: Will the Steam Engine Replace the China-Man?
Let me be the first to say: I for one welcome our new antihyphen overlords.