There are a lot of *.amazon.com internal subdomains used for employee resources and infrastructure. So I think they just want to keep that reserved for very specific things
I was curious as well. Especially as I thought they'd been allocated the .amazon TLD.
The SSL certificate was issued by Amazon, so it is legit.
Does that matter? i mean they are running their own CA for use with their offerings on AWS. I am not sure if it is the same CA though.
EDIT: Just checked it and it is the same CA they use for AWS services.