Maybe the fact that in certain regions, the cost of soda is outlandish when not on sale. For instance, in the Bay Area you can walk into most grocery stores and it will be somewhere in the neighborhood of $4.49 for a 12-pack and $2.49 for a six-pack (when not on sale). Anything around $3.00 12-pack is a good deal and occasionally you're lucky to find a 2/$5.00 (as opposed to other areas where I've seen it as low as $1.88 12-pack on sale Coke or Pepsi products)
The $0.99 6-pack deal is usually a good time to make a trip to Fry's (before they run out of stock on the Diet Coke).