I disagree. You could make the same argument that texting and phone calls are handled by smartphones, so why need the apple watch? I personally hate looking down at my phone to navigate while walking around in an unfamiliar city.
If there was a big demand for pedestrian navigation (walking around an unfamiliar city is not a frequent activity for most people) we would already have better solutions, such as good voice navigation, which would arguably be better than can be done on the low-res Google glass display.
Receiving messages and notifications is a very frequent occurrence for most people these days. Personally I suspect I'd find the watch notification preferable to one that appears in my peripheral vision (disrupting attention) for that use case.
Good pedestrian navigation (which needs pedestrian road/pathway networks that haven't been built to the same extent as they have for roads, though in some countries like Japan they are much better) doesn't need constant interaction.
You'd just be wearing your regular headset and you'd occasionally hear "at the next intersection, take the traffic light on your left, cross the road and continue down xxx street"
