Since an ECM only purchases materials for the components they produce, they are able to purchase in bulk offering the OEM substantial cost savings. And since they are purchasing from their individual supplier in greater frequency, the manufacturer takes advantage of the strong relationships developed.
Finally, the contract company will thoroughly test the components they provide for quality. They will stay at the forefront of technology proposing improvements and upgrading their product so that it works better, lasts longer, and is more efficiently. This is a daunting task for the original manufacturer that has hundreds of components to keep up with.