I think that many devices can fall between multiple sectors. The way I look at it to understand why certain devices go to the Center for Devices and Radiological Health, the Center for Drug Evaluation and Research, or the Center for Biologics Evaluation and Research is to take away one aspect of the device and then the other to see which is the primary mode of action. For the example you gave, a device that slowly releases a specific drug at a controlled rate, although the controlled releasing rate is an important factor if the drug was not present then the releasing device is pointless. If the drug was taken out of the picture then there would be nothing for the device to release.