The reason they were so aggressive about forcing Prime onto people was to engineer the behavior into people of buying from Amazon by default. Rather than ask questions about where's the best place to buy.
For something I can get at Best Buy, for example, I wouldn't buy online and wait for shipping, I use their price match (if I need to) and get it same day. And often when I look up the same item at different online retailers, the price is the same or one site undercuts the other by a penny. Not a coincidence, they all have to stay competitive.