Re: Not an entirely fair comparison
...both the Amiga and Atari ST had large portions of their OS's in Rom
True, however bear in mind that early TOS versions were only 192KB in size so even factoring that into account, the ST had a total of just over 700KB for the OS ROM and working RAM. The screen memory had to come out of that too, reducing the available memory by a further 32KB.
Furthermore, very early ST's had to load TOS into RAM from floppy disk, and some ST models were released in Europe with only 256KB RAM.
The same is true for very early (KS 1.0) Amiga's - they had to load in Kickstart from floppy and still only had 512KB to play with.
In all cases, they were still capable of much more than Windows 1.0.