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.
sendgrid is like 5 years old: http://sendgrid.com/
mailchimp's version: http://mandrill.com/
rackspace: http://www.mailgun.com/
also: https://postmarkapp.com/
SES is still the cheapest (especially when scaling up) and extremely fast from my experience with it.
Here is a good article I found about SES and competitors such as Mandrill: http://www.ventureharbour.com/transactional-email-service-be...
(First used MailChimp in 2003 and they've always been the bomb.)
The Mandrill service is nice, I agree.
Also, MailChimp has a very cool 404 page: http://kb.mailchimp.com/article/transactional-reports-overvi...
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.