jackrae: I hear you. It is always easy to complicate matters.
If Vo = Vi then that's great.
Look at it this way: Vi and Vo are connected via a wire (of zero resistance). So Vi cannot differ from Vo.
Now, if Vi is the specified voltage on that battery with high output resistance, it gets slightly more interesting. But a regular battery / power supply will have output impedance far lower than that resistor's (2490ohm) so even if they differ, it is immaterial.