Many companies don't even sell their products directly. Others sell them in higher prices than resellers. This is required for large companies to help resellers. If Nokia was selling N900 cheaper than a reseller then there would be competition between Nokia and the reseller.

Nokia depends a lot on e.g. stores and would never risk competing with them. That would result in reduced product advertisement, push and (finally) sells, because the stores would instead sell another product or a product of another company.