Walmart wanted to take over the gasoline fill-up market. What could be more convenient? Instead, gas stations have thrived living near Walmart, because convenience doesn't always maximize value. Gas stations draw people with gasoline, and make money on in-store purchases; that model didn't work for Walmart, because gasoline doesn't draw people to spend an hour shopping at Walmart, so the value-add was non-existent.
The notion of extreme convenience fails as often as it succeeds in my opinion. It's why Walmart doesn't own every category. It's why GameStop exists. Specialization can just as easily trump maximum convenience, you have to offer enough of a value proposition. It's why Starbucks and Apple Stores exist; it's also why dollar stores are thriving. It's why Dunkin Donuts and Krispy Kreme exist despite Walmart selling donuts.
Obviously Walmart doesn't manufacture the drugs in the prescriptions; they don't have a banking license; they don't make movies or games; they don't cut your hair; they don't run the food franchises (eg Subway); they don't make furniture; they don't make the groceries.
Walmart is merely a retailer, and with their physical space they sometimes act like a mini mall. They don't even own their shipping network any longer. That is not Walmart being everything to everybody. Quite the opposite, they're admitting they can't be, so they let other companies ride their coattails to optimize their sales per square foot.
What I said was that for a lot of people, Walmart is where they go for nearly everything. There are a lot of places in small town America where a Walmart moved in and a lot of the existing local retail and service businesses shut down. It doesn't have much to do with positioning or branding. It's just really easy to get everything done there.
The point is, it's possible. If Walmart can do it, maybe Facebook can too.