For Kickstart 3.1 there were different versions for different hardware because there wasn't enough time to fix all the bugs (they'd fix one and it would break something else) and also due to rom size (A4000T needing both scsi & ide for example). They could have pushed workbench.library onto disk for everybody and included all the devices with auto detection, but there wasn't a business case for it.
Thats not true.
There are different hardwarespecific versions of exec, expansion and devices.
The A1200,A3000,A4000 & CD32 versions are 020+ optimized .. not working on 68000.
The A3000 is very special .. the ONLY rom with real FPU-code inside !!!
A600/A1200 includes some PCMCIA-code.
A3000/4000 includes "bonus" for onboard fastmem.