Sadly, I'm guessing all this is going to be moot before too long. The golden age of consumer GPS is gone as smart phones have taken probably 95% of that market with a free app on a phone you were already paying for.
For use in a car, yes, I agree. I ditched the two other car-Garmin units I had as Google Maps is so easy to use in a cage. My recent trip though convinced me there is still a place for a GPS on a motorcycle. In fact, the Garmin is better and more functional on a bike that a phone is.
The single feature that leads me to this is how well it works with gloves on. When I was using my phone for bike navigation (which means over the last three 1/2 years), even with smartphone-compatible gloves on, it was always a chore to interact with the screen, even when stopped, as the "buttons" are usually really small. On the Garmin, the "target" you need to hit is much larger and the technology in use (pressure sensing rather than capacitive) doesn't depend on skin contact, so typing out an address, switching to a weather radar overlay, skipping songs, and checking trip-computer type functions are totally doable without having to remove my gloves. I would not do any typing on the move of course, but I could do simple interactions while riding, with my gloves on, without compromising safely (on highways or non-twisty roads with no traffic). With a smartphone? Forget it, that would be a death wish.
Besides, I put huge stock in keeping my cell phone on my person so that if I get, eh, "involuntarily separated" from my bike, I will have my safety line handy. Dragging oneself across the ground with a broken femur I hear is quite painful...