I'd dispute both cost and knowledge.
If a store is close to your commute route, for example, the delivery costs will probably never be low enough to match with that.
I would also dispute on knowledge. In this case, knowledge is a matter of time: you can always google exactly the product you need, but that's going to cost you time. If you're not sure about the exact specifications of what you need, reading reviews isn't necessarily going to help either. Salespeople, if available, can tell you what you need and what's the best cost-benefit (probably leaning towards the more costly).
There's an additional aspect you didn't account for: entertainment. I don't get entertainment off of shopping, but i know a lot of people do. You get some of that while looking things online, i.e. 'browsing' items, but it's not the same experience. Also, shopping is often tied to other entertainment like eating out, movies, etc -- this is done strategically for mutual benefit of mall venues -- and of course can't be replicated online.
It's easy to imagine even if the whole catalog of Amazon were available today for 1-hour delivery for $7.99 (or less), a big part of the average urban dwellers' shopping would still be done offline.