There is a slideshare about their networking approach for VPC somewhere it's quite clever. But I can't find anything for EBS and what features it might have that make Aurora replicate the way it does.
I remember what it looks like, tried to Google it but can't find it. The gist of it was that they didn't create any tunnels or VPN like infrastructure to create VPC, because it wouldn't scale to large numbers of nodes. Especially because your servers can be on completely different hosts all of their internal network.