I think he meant, why _remove_ the old syntax instead of supporting it _in addition to_ the new syntax?
I can't see any good reason not to support old syntax as backwards compatibility.
Hmm, as a user that makes sense. As a programmer, it does not. There's nothing like adding "backward compatibility" kludges to add bugs to your code. Bugs mean extra work for the developers, work that could be better spent fighting spam.
You'll find that most OSS packages will sacrifice backward compatibility in favor of maintainable code and fewer bugs to work around later. I know it's a bit of a pain, but the general OSS mindset of breaking backward compatibility is what allows most projects to progress forward.
One or two of these hacks isn't so bad, but once you start down that road you eventually get bound up by having to maintain hundreds of hacks, kludges and other garbage in your code that users who still have config files from 20 years ago need to run their systems.
The "always maintain compatibility" mindset of the windows world is convenient for users, but really slows down development progress in the long run, and in some cases completely prevents product improvements. It's a very bad mindset to be in. Even the windows world is starting to move away from it by obsoleting older versions of products.
As for breakage, SA has a long history of doing this. This is by far not the first time.. ie: report_safe.
The Linux kernel does it all the time to their low-level interfaces.
Bind has done it to their zonefile formats.
