In reply to Slay_Hive.

Legend B, Mariah after her 11th year received 4 albums that were platinum/multi platinum. 2001 greatest hits 1.1million, 2002 Charmbracelet 1.2 million, 2005 emancipation of Mimi 6.2 million, 2008 E=MC2 1.2 million, her 2001 glitter soundtrack sold 0.652, 2009 Memoirs of and imperfect Angel 0.529.
With that decade Beyonce sold over 11 million and Mariah over 10 million.

Also beyonce wasn't close to being the biggest selling artist that decade. Britney Spears sold more, Alicia Keys, Eminem, Usher, Nelly, Jay Z, 50 cent, N Sync, Norah Jones, Linkin Park, Creed, The Beatles, kenny chesley, toby Keith, tim mcgraw. Just to name a few.
Beyonce is very successful, but she's not a big selling artist.