Zipcar is really a great concept, I've used it many times. That said, the author forgot to compare on one key segment: price. And that's where the companies differ in their model. Zipcar is about $75/day, where most rental cars are significantly less than that. But you cant rent them by the hour. And Zipcar wont come pick you up. And Zipcar charges a membership fee.

There is a place for both of these companies in the market, so a comparison like this is kind of like comparing chartered flights to Southwest. That's not to say the big nationals couldnt learn lessons from zipcar, like the audio jacks, reasonable insurance plans, etc.