See those extra Lego pieces? Those are the ones most likely to be lost either by the manufacturing process or by accident when a kid (or I) build the thing.
Meanwhile, I’ve purchased plenty of build it yourself furniture from places like IKEA or CB2, and they almost always leave out a 2¢ screw. And it’s almost always some special screw that the local hardware store doesn’t have. Fun right?
Note that leaving out a 2¢ part is worse than a big all-at-once failure. With a big failure both you and the store know how to fix it. With a missing screw failure you think, “can I live without this screw or do I drive all the way back there with a half-built book shelf because they screwed me to save two cents per unit?”
Penny wise, pound foolish.
The user experience design version of this is “not going the extra mile to make the experience frictionless.” Yes, it costs more to do, but the downstream effects are huge.
Related Post: Augmented Reality at the Lego Store.