Very, very few cities in America are walkable enough to enable the average household to not own a car without it being a hardship [1]. You can probably count them on one hand.
So yes, Denver has a few walkable areas that are nice. But if you can only walk 80% of the time and still have to own a car for the other 20%, which has to sit in a parking spot somewhere all the time, then we're back to the subject of this article.
1. I'm not saying it can't be done, but if you have kids, or aren't able-bodied, or don't want to spend 3x - 5x more time on public transit than you would in a car, or live in an area with extreme weather conditions, or don't want to be weird-sweaty-bike-person all the time, etc, then you need a car in most of America.