Except, if it is made in a factory you have:

• Transportation costs from factory to store • Cost for additional space required to hold stock

If it is sold through a store • Cost for display space in a store • Cost of a sales person selling the item • Cost for (neat) packaging • Cost of your time picking up the item

etc.

So while the factory can logically create the product cheaper it could still end up costing more.

I agree that posting and packing are always going to be a factor. The other points you mention are becoming less relevant as we move towards online buying. This is especially true of shops selling random obscure parts. Also, just think about how annoying normal 2d printers are. Sure you can print something at home; but it will be expensive and slow compared with the expensive laser printer at the office.

I know a biker would go for the weight savings of carbon fiber but check this out. Carbon fiber reinforced prints:

http://www.thingiverse.com/thing:91464

http://www.youtube.com/watch?v=p1yOf6Ba1ts