Apple continues its relentless march to the top of an ever-decreasing heap:

Apple today announced that iTunes (www.itunes.com) is now the number two music retailer in the US, behind only Wal-Mart, based on the latest data from the NPD Group. Apple also announced that there are now over 50 million iTunes Store customers. iTunes has sold over four billion songs, with an incredible 20 million songs sold on Christmas Day 2007 alone, and offers the world’s largest music catalog of over six million songs from all of the major and thousands of independent labels.

Big numbers. But it's odd to me that this is happening while iTunes isn't the best online music service (that accolade would go to Amazon MP3), though the iTunes Store is a tremendous place for podcasts, TV shows, and rentable movies.