Super-luxury car sales dropped in 2013

You can be forgiven for thinking that the global supercar market is running at top speed.

After all, the rich are getting richer, and the population of millionaires and billionaires is hitting new records. It also seems like we see a new $1 million car or a new member of the "200 mph Club" every day. The media is filled with stories of how conspicuous driving is back in style.

But some new numbers reveal a different picture. According to Bentley Motors, the world's sales of cars priced at $200,000 or more actually fell by 6 percent last year.

The main problem: China.

Bentley Continental GT Speed Convertible
Source: Bentley Motors

While Bentley, a unit of Volkswagen, doesn't break out industrywide sales in China, it said Bentley's own sales in the country—its second biggest market after the U.S.—fell to 2,191 cars from 2,253 in 2012.

(Read more: Amazing supercar experiences)

Bentley's global sales chief, Kevin Rose, said China's weakness is owed to "misplaced investment decisions, a slowing economy and the migration of high-net-worth individuals from China."

He said he doesn't expect 2014 to be much better. The U.S., on the other hand, had a banner year, with Bentley's own sales up 28 percent from 2012.

(Read more: My test drive of the world's fastest car)

Bentley's overall market share grew 3 percent in 2013 to 25 percent of the supercar segment.

Granted, some top supercar makers—like Ferrari—deliberately sold fewer cars in 2013 to preserve their exclusivity. And the decline could be owed in part to the timing of model launches. The supercar market category includes Porsche, Ferrari, Lamborghini, Maserati, Bugatti, Mercedes and others.

(Read more: Ferrari cuts production: Slump or strength?)

Yet for now, 2014 is shaping up to be the year that America dominates luxury sales—whether it's for Bentleys or Birkin bags or penthouses.

—By CNBC's Robert Frank. Follow him on Twitter @robtfrank.