Seems to me that Amazon has been quite busy innovating and expanding their feature set.
Why are you going to switch from the other providers to Amazon? Because of price?
Having tried the service it's currently clunky and command line based too! I wouldn't actually call these comparable products. SES seems more like it replaces transactional emails that users might have previously event sent without a lot of a anti-spam measures. The value that companies like Sendgrid/Mailchimp/Postmark add outweighs the price for me and, at least, in the short term I won't be moving anywhere.
I am a sendgrid customer, and unless Amazon is cheaper and can solve the deliverability issues, there is no way I'm switching.
Sendgrid is $0.00045 at the highest tier which is $0.45 for 1 thousand.
That means Amazon is much cheaper even at Sendgrid's highest tier, further, it's much cheaper at the lowest tiers as well.
Sending email out is quite important for growth, and such services really help businesses.
What impresses me about amazon is that they are not looking at what the competition is charging or trying to charge high based off the fact that there are not too many such services, but are simply providing the service at a reasonable price.