For those of you who are wondering why so many of his albums popped up in the charts only on December 5th, 2009, months after his passing, it's because up until then, Billboard had a strict rule that any album that has spent at least two years on the Billboard 200, would automatically drop out of the chart for good once it had fallen out of the Top 100.
From then on, it would be relegated to Billboard's Catalog album chart. But since demand for Michael was so immense, they decided to change the rules and since then, any given album is listed on the chart, be it current or catalog.
So now you have your Dark Side of the Moon popping up in the charts back again every once in a while, adding some more weeks to its record tally, the occasional Beatles album, or some other perennial classic loitering around, such as Thriller.