If anything, AWS is overrated. It already has some decent competitors and more will grow up soon, though they're massively underutilized. The idea that Amazon itself is critical to internet infrastructure is very disturbing, yet in many cases, it's true these days. We really need to get other cloud providers in the mix.
Amazon as a retail store has been consistently great for me in all major aspects. Any issues I've had with orders have been promptly resolved and Amazon has gone to bat for me several times. I agree that Wal-mart or another major department store could give Amazon a run for its money if they played their cards right, but like you, I don't think they're in that headspace.
SES is really the only AWS service that has not been done by anyone else as far as I know. Some of the SES features (spam reporting for instance) requires cooperation between email service providers and Amazon, something that many other companies would have difficulty arranging.
Yeah, the issue isn't really that there are no similar services available, it's just that people don't really use those services very much. There are several search engines competing against Google too, but if Google blackballs your site and you're dependent on organic search traffic, you're still going to lose 90% of your visitors overnight.
Internet infrastructure is pretty important, so it's a little more disconcerting to me if some huge percentage of sites are dependent on the same single ISP/datacenter/etc.
Amazon as a retail store has been consistently great for me in all major aspects. Any issues I've had with orders have been promptly resolved and Amazon has gone to bat for me several times. I agree that Wal-mart or another major department store could give Amazon a run for its money if they played their cards right, but like you, I don't think they're in that headspace.