I felt like adding to that...
This sometimes leads us to stupid package sizes, like Nathan's hotdogs coming in a pack of 14 (now THAT is a wtf) , 7 oz packs of things like butter and cheese, etc.
Also sometimes one major brand makes those moves and a competitor refuses to follow. A great example is Haagen-Daz reducing their "pint" to 14 oz and Ben & Jerry not doing the same, in fact even taunting Haagen-Daz by printing "Still 16 oz" on their wonderful, delicious ice cream. This puts the retailer in a position of putting the $4.99 Haagen-Daz next to the $5.49 Ben & Jerry's and letting consumers figure it out.