I think the lesson is: the front end is the most important part.

Think about running a restaurant. You have to order ingredients in a timely manner. You have to get supplies and consumables such as utensils. You have to deal with the lease. You have to pass health inspections. And so on.

And does this customer writing his review mention any of this? No.

It's really easy to get caught up in back end stuff. What web server are you running? What language is your app in? Memcached? MySQL? CouchDB? Functional programming? Etc.

Certainly, you have to have a decent back end so that you can have a front end in place. But your clients review the quality of the front end, regardless of what's behind it.