If anything, I would say 1.3 was written for A1200 users.
I agree. It first appeared soon after the A1200 appeared and is the easiest way to get many older games to work. But it does also get some very old OCS games working on an ECS A500+ or A600, so maybe the software started development for this reason first.
If you haven't played a classic game in years, it's never too late to start!