They are not ROMs. They are images of game disks.
Consoles (like the Sega Genesis or the Nintendo SNES) stored their games on ROM cartridges. So, when a console game is dumped it is often referred to as a "ROM".
Computers on the other hand, (such as the PC, the Apple Mac, or the Amiga) store their software on disk, or on CD-ROM, or more recently DVD.
Certain computers (such as the C64, Vic-20, or the Atari 800) did have a cartridge port which could accept games on ROM cartridge but this made the games very expensive to produce and so most games were on floppy disk or on cassette tape.
If you download some software like this it is not a ROM. The only "ROM"s ever available for Amiga is the kickstart ROM. There is a (broken) link to kick1.3 on that page but you seemed to be referring to the disk images...
If you download a game for your PC do you call it a "ROM"?
EmuLamers coming on Amiga IRC channels begging for "Roms for playing on Amiga emulator" really p**s me off, sorry.