You should not have copper joined directly to galvanized. You will get corrosion. There should be a dielectric fitting between the two. I would replace the shut off with brass. As a side note, it is always a good idea to close the shut off valves when your washing machine is not in use.
If its been this way for a long time don't worry about it. If you do not see corrosion now and its been that way for a long time why worry. I think it may have something to do with it being at the end of a line and no path to ground across the two dissimilar materials that is why you don't have corrosion. Just a guess.