You can be successful on AWS, but you're leaving money on the table, and for relatively commodity services it's just a question of time before a competitor realise they can do the same with much better margins and lower prices elsewhere.
If your hosting is a small portion of your costs, that might not matter, so I have certainly run services on AWS too, and do in my current job as well, but it's a very expensive convenience. I've yet to come across any systems I know the internals off that couldn't cut hosting costs by moving off public cloud services.