Why does my 3-way dimmer circuit show low voltage on one traveler or the other?
This is indeed normal. Modern, high-impedance voltmeters can measure voltage that has no actual "oomph" behind it. What you are seeing is a capacitive "phantom" voltage coupled to the inactive traveler from the active one.  If you have a Low-Z range on your voltmeter, it will indeed not show this "phantom" voltage, nor will it be indicated by an electrical voltage tester ("wiggy" or equivalent device).