[rsanders]

I probably use 20-30 apps that support using S3 that I can think of right now. Not all of them are maintained by me or even open source. Other than a proxy, it's impossible for me to change some of them.

In terms of use case: my company has a customer that requires us to locate an instance of our product in Azure, and some of that infrastructure is much easier to move with a compatibility layer.

You might as well ask why there are any standards in software and networking at all, as each new protocol or library isn't THAT difficult to support.