Why batteries aren't included

From my word-a-day email:

From: Tyler Kenney (tyler.kenney mattel.com)Subject: Batteries not included
Speaking as a member of a large toy manufacturer, those $2 batteries wouldend up costing you at least 3x their price if included. The manufacturertakes their hard cost and adds their margin, then the retailer does as well.If the batteries don't need to be in there, it's better for all parties.----------
From: cafewalter (from bulletin board http://wordsmith.org/board )Subject: Batteries not included
I'm a (very small) manufacturer of battery-powered devices. Although I do ship my goods with batteries, I have some insight into why others might not. One big reason is that they're HEAVY. It adds substantially to the shipping cost, and also to the risk of damage owing to sudden acceleration (bumpsand drops) during shipping.