You are seeing different results than me. This depends among other things on your location (also probably which data center served you the result). The number of pages in index for a large site can even differ depending on the time of day (About n results).

http://www.youtube.com/watch?v=6g8MJKFSWJU (Matt Cutts answers: How reliable is the site: query and why does the total count sometimes change from page 1 to page 2?)