The music industry has been stuck in a rut for nearly a decade. But every once in a while, it still manages to produce one of those unstoppable hit albums that give everyone that good old feeling.

This year's model is Adele's 21, which not only sold more copies than any other album in the U.S. in 2011 (more than 5.6 million to date), but which has also moved the most units of any artist since 2004. According to a Reuters report, those gaudy figures (which top 15 million worldwide) make the British songbird the first artist to cross the 5 million mark in one year since Usher did it with his fourth studio album, Confessions, which sold 7.9 million units more than seven years ago.

And to think she did it by releasing just two mega singles, "Rolling in the Deep" and "Someone Like You," and barely touring North America due to recurring vocal issues.

There have been other big hits along the way to Adele's mark, including Eminem selling more than 3.4 million copies of his comeback Recovery album last year and Taylor Swift taking the honors in 2009 with Fearless, which sold 3.2 million copies. But none have come as close to Usher's mark in the interim.

There doesn't seem to be any chance Adele will be surpassed by the end of the year: The closest contenders are Lady Gaga's Born This Way (2.08 million) and Michael Bublé's Christmas (2.4 million). The other good news is that overall music sales are expected to be up slightly (3 percent) by the end of this year, marking the first time that's happened since 2004.