Sure the margins are lower in online retail, but even then Amazon is performing abysmally, and the trend in almost all their numbers is downwards. The only reason they are still around in the first place, is sheer size. Smaller retailers would never survive on the profit margins Amazon is producing.
The thing that sticks out most from their earnings release is that the trend is clearly downward. The profit margins and net cash flow are sinking, while operating costs, number of employees, etc are rising. Added to that, their market cap/stock valuation is truly insane, which IMO is a ticking time bomb.
What this all means is that Amazon is going to get in a shitload of trouble somewhere down the road. Remember that they only made about $5 billion in profit over their complete lifetime, of which only about $1.5 billion is left after deducting losses, so in terms of cash Amazon is more or less on life support of their investors. All it takes is some relatively minor event (more focused competition, lower consumer spending, some kind of bad media attention) and their stock will tank, and the whole constellation could go down like a house of cards.
No matter how much you like Amazon and its services, it's hardly an example of a solid business if you ask me.