Can anything slow Apple's (NASDAQ:AAPL) advance in the digital music market? Yesterday The Wall Street Journal reported that it took only four days for the new iTunes Music Store in Japan to rack up a million downloads. That's the fastest launch in the history of the service, now found in 20 nations worldwide.

Not that this should come as a surprise, mind you. According to the Journal, the iPod is already a major hit in Japan. But the iPod has been equally successful in the U.S., and it took a week for Apple to sell 1 million downloads here.

Barely a week into its existence, iTunes is the top digital music store in Japan -- without any music from labels owned by Sony (NYSE:SNE). That's right: The company that birthed the Walkman -- and also happens to own one of Japan's largest and most popular record labels -- isn't yet distributing songs through iTunes. That could relate to Sony's own line of would-be iPod killers, including thiswhatchamacallit, or to its ownership of a rival digital music store. According to the Journal, Sony's Japanese venture typically sells 450,000 songs each month.

Apple just did that in less than 48 hours.

Impressive though that is, Apple's stock remains expensive. Still, many of you don't seem to care, and the Rule Breaker in me wonders whether you really should. After all, won't it always be expensive?

Apple has been a hit before, and it is again. The company has also dropped to the bottom of the charts more than once, and will again. You're welcome to your opinion, but I wouldn't bet on that happening anytime soon.

Download further fruity Foolishness:

Digital music. Satellite radio. Advanced therapeutics. They're all technologies poised to change the world. In search of the next ultimate growth stock, David Gardner and his merry band of Fools cover the companies behind them each month in Motley Fool Rule Breakers . Get in on the action today with a risk-free trial.

Fool contributor Tim Beyers enjoys sweet music through iTunes -- on his G4 PowerBook, natch. Tim didn't own shares in any of the companies mentioned in this story at the time of publication. You can find out what's in his portfolio by checking Tim's Fool profile, which is here. The Motley Fool has an ironclad disclosure policy.