Mostly, it is a sales ploy by Garmin. Like Reinhart said, how many roads change in a year? It's "only" $99 for this year's update if you are so inclined. To update it, you will need a USB to mini-USB cable to connect the device to your computer. Garmin's website will do the rest ...
Speaking of which, I love my Garmin 350. I turn it on in "off road" mode on airplanes to get our location and airspeed (the highest I have seen was in a Boeing 767 ... 656MPH). I have used it all over Mexico, St. Thomas, St. Lucia, Barbados, Bahamas, Jamaica, Alaska and Canada, not to mention a different city that I am in for work every week ... all without fail. I have used it to set way points on Lake Mead for fishing, and off the coast of Mazatlan in the Pacific and off the coast of Cabo in the Sea of Cortez for the same. I have used it to find hotels, airports and restaurants. I have sought "treasure" by geocaching with it. Of the trillions and trillions of dollars the DoD has spent, next to the deregulation of the internet, I think the GPS has had a tremendous impact and I truly could not imagine my life without it.