Number of Spots on BJ Table

When I played blackjack quite some time ago, I always *thought* the number of spots on blackjack tables were seven. I recently started playing again (about a year ago), and I've realized that the number of spots actually varies from 5 to 7. (Is the casino trying to reduce the players' edge by eliminating spots?) Does anybody know the "theory" behind the number of spots on blackjack tables (that is, if there is any)?

~Black Jack in the Box.