Wolfram Alpha tells me that $399 in 2001 is $498.06 today.
Two things changed after the iPod 1) they successfully began competing on lower price points as well, eventually capturing 75% or so of the MP3 market and 2) they began releasing products that undercut previous products, think Apple TV and iPad.
The big question for Apple's future is whether they will be successful in competing on the low-end of the market or be pushed back to the high-end only by Android and others.