Where are you that this is true? This is directly opposite of my experience. I genuinely can't remember the last time a Prime/2-day shipment was delayed. In fact, I'll routinely and deliberately pay a premium to purchase something via Amazon Prime (both within Amazon and across internet vendors) precisely because of the confidence I have in their shipping reliability. No one else comes close, frankly.
That said, in fact I don't tend to buy BestBuy-style products at Amazon very often, precisely because these things are available at competetive prices at retail. Amazon wins for things I don't feel like "shopping" for.