Why does it matter whether the current is going through a resistor or not? It still is current, and current in a series circuit is the same everywhere. Regardless whether it is coming from a voltage source, current source or potato battery.
Good question. The answer is that the results due to the behavior of a device will be different depending on whether it is driven by a voltage source or current source. Take a resistor in series with other components, for example. If it is driven by a voltage source, and it increases in value due to temperature changes, it will take more voltage for itself, and the remaining components in series with it will have less voltage. If it is driven by a current source, the rest of the series components will not be affected by the change in value of the resistor.
The changes can be more profound if the voltage or current source drives a active component like a BJT.
Ratch