Wong, that was funny. Seriously, I got a good chuckle out of that.
Living car-free is most definitely not a utopia. The people I know do it either for cost-saving or environmental reasons, or a combination of the two. Living with 1 car per household is more doable, and entirely reasonable for people downtown if they do not have 2 jobs that require driving.
Let's not underestimate the increasing trend of having things delivered, especially in urban areas. We're not just talking J Crew mailorder here. Liquor, milk, produce, groceries, coffee makers, socks

What doesn't amazon sell? Amazon prime is free 2 day shipping. Here's an example, I needed a new water filter for my Samsung fridge. The only place that I have found them is Lowe's. I used to once a year drive to Lowe's in Lakewood since the Lowe's off of Alameda in Denver closed. I would buy 2 water filters at like $50 apiece and be good for a year. This time, I ordered two from amazon for about $35 each, free 2 day shipping, no more than 2 minutes out of my day. That my friend is the wave of the future. Just look at Lowe's and Home Depot: they themselves have set up expensive web stores. The web sales side of most retail business has been the sector that has grown, usually at some expense to the brick and mortar. This will enable more city residents to have items at their fingertips quickly, even if Union Station never has a home improvement store. These services are not a "preferred substitute" for retail, they will ultimately work in conjunction with brick and mortar stores in downtown.
With that being said, more and more retail is, in fact, coming to downtown which will provide even more of the multitude of products that we would desire and/or require. Realistically Denver is not big enough to support many of the retailers having two locations, and frankly, Cherry Creek is a great location from a business standpoint and is well established. When the need arises, a downtown resident can easily get to CC to go shopping, whether it be by car, bike, bus, etc. It was only a mere 4 years ago that the whole Union Station buildout was just starting and look at it now. We are not pining for some utopian car-free city 20 years from now. The infrastructure for a great downtown is being laid as we speak, and with it will surely come more retail. As you admitted yourself, just since you lived downtown, Denver has added car share, bike share, and ride share.
Car-free living in Denver? I am not sure anyone is really saying that is realistic for more than the niche group of hardcore people. Having to use a car for the majority of your daily needs living downtown? No, I don't think so.