I think you really have to understand that at its heart, Let's Encrypt is not about free certs as much as it is about automatic certs. If you just want a cert, definitely use an established provider. But a year from know, LE will be making this a "set and forget" thing, which is how it should be. LE is NOT a painless way to get certs for legacy infrastructure. I found this out by using it for an elastic beanstalk hosted site. I just wrote about it at https://go-to-hellman.blogspot.com/2015/11/using-lets-encryp...
You nailed it. It's important that our certs be free because we can't automate a billing interaction. If we had to charge then sysadmins couldn't just type a command and be on their way. Automated renewal could fail because billing info was out of date. This stuff has to just work, reliably, if we're going to expect the entire Web to use TLS.
On the plus side, Amazon could choose to automate IAM SSL storage and renewal through Let's Encrypt so it would be fully automatic. Might take a bit until they do that though...
