Deborah,

You're right that having a point of differentiation isn't enough. The underlying concept, offering, and execution has to meet a certain standard before the point of differentiation really comes into play. 

As an example, I often think about a store that opened while I was a college student in Tucson. It was a yogurt shop/self-service laundromat. The concept was that while you waited for your laundry to finish, you might want some frozen yogurt while you waited. 

The problem? The place wasn't particularly clean and reeked of lint. I don't care how good your oreo yogurt is - if I'm smelling detergent while I'm eating it, your point of differentiation just doesn't matter much.

Thanks for the post,
Brad