Earlier quoted context omitted.
All proprietary APIs. Also not all APIs are as critical and large encompassing as the whole backend code of your business.
Many are very critical, and many are not proprietary. Databases and web frameworks are two that come to mind immediately, yet people seem to choose those based on the number of blog posts about them. And almost all APIs are vulnerable to reimplementation. With Parse's API, it would theoretically be possible for another project to implement an identical interface to their backend, and allow you to simply change one Lo…
PostgreSQL 9.3 is installed on your database server, the source is available, and it isn't going anywhere.
If Oracle discontinued their database platform tomorrow (unlikely!), your licensed copy will remain valid for a long time up until you swap it out for another closely compatible database.
If Parse closes their doors or exits tomorrow, that's it.
Compare to AWS: If Amazon discontinues EC2, other virtual hosting services exist. If they discontinue Beanstalk, then at least you were coding to a commmon servlet API. If they discontinue S3, there are some compatible competitors, but hopefully you wrote your data layer to be S3-agnostic.
I think non-standardized AWS services are more risky. More standardized fare -- EC2, Beanstalk, etc -- less risky. Basing your entire code base on pervasive use of Parse -- very risky.