What elses on the list then would be interested to know.
Most AAA titles are placed on it for the first month of sales.
Skyrim however is a niche game. The market it appeals too drops after the first few weeks, its not as wide scale as other current titles, So off that list some are chosen to lure people into the store by lowering the price during the sales.
Statistically, people will buy 2-3 more games at the same time if they believe they are getting value. If they come in for something particular, they will see this and buy it ontop of their point of visiting, thinking its good value.