Where products have complements, companies will charge a premium price since the consumer has no choice.
For example a razor manufacturer will charge a low price for the first plastic razor and recoup its margin (and more) from the sale of the blades that fit the razor. Another example is where printer manufacturers will sell you an inkjet printer at a low price. In this instance the inkjet company knows that once you run out of the consumable ink you need to buy more, and this tends to be relatively expensive. Again the cartridges are not interchangeable and you have no choice.