Webvan wasn't the first ever grocery delivery service. Their failure doesn't make in non-viable, it just means they didn't do it in a viable way.

I still see the dairy truck and the Schwan's truck in my neighborhood from time to time. They're not exactly the same thing, but they've proven long-term sustainability for some parts of the market. I also see home delivery trucks for King Soopers (Kroger) and Wal*Mart in my area.