Plummet 4 percent? I don’t think so…

I caught this headline on Reuter’s today:

Retailers’ holiday sales plummet 4 percent

Now, I’m sure that a 4 percent drop in sales is painful for retailers in these tough economic times. But sales can’t “plummet” 4 percent. Dip, drop, fall, slump, sure. But to plummet is “to drop sharply and abruptly” (Merriam-Webster), and 4 percent is just not that sharp a drop.