IMHO, your analogy is exactly correct and if Safeway was as big as Amazon, Warren would be calling for them to be broken up too.

On the other hand, maybe the analogy isn't good because safeway displays products side by side while Amazon can more easily promote their own products. Level on a shelf has much less effect than a product being out of sight at the bottom of a webpage or even the second page of search results.

Grocery store margins are razor thin though, they compete with each other a lot.