British singer Adele reached a milestone of sorts this week when her album "21" logged its 16th week at the top of the Billboard 200 albums chart.  It is the longest reign atop the chart for an album since the soundtrack for "Titanic" spent 16 weeks at the top in 1998.  Since SoundScan began tracking sales in 1991, only five albums total have spent as many as 16 weeks atop the Billboard 200, including the soundtrack for "The Bodyguard," which spent 20 weeks on top in 1992 and 93.