It's not about the distance. It's about the number and diversity of things that you have access to.

If you have access to 10 identical Chuck E. Cheese's restaurants with a 10 minutes drive, you have less access than if you have access to 10 very different restaurants with a 10 min walk as it's typically the case in a dense city center.

I agree that the relevant metric is time. In a dense environment, you typically have access to more and more diverse things than in a less dense, car dependent suburban environment, in the same amount of time.