alt Hacker NewsI think backing services as attached resources was opposed to the practice of having your DB, and cache, and whatnot managed and maintained by a completely separate team and not really treated as part of the application. Even the schema changes.
The port binding was really a response to tomcat or modphp being modules in the webserver, as opposed to hosting their own web service internally. This was before nginx took off, and proxying to internal application ports was common.
edit:
I was wrong about the backing services, it seems it is really about treating them as configurations and being able to swap them out without making code changes.