Why must interpreters be stored in ROM whereas compilers need not be stored in

Lets think about how these two types of language translator work. A compiler converts the entire program into machine code. This machine code version can be saved and run without any need for a translator. It could be saved on a floppy disk or CD and transferred to a different computer without the compiler software at all and it would still run. An interpreter translates the program as it is being run. This of course means that the interpreter must be in the computer?s memory at the same time as the program is running. Not all interpreters are based in ROM but they do need to be present in order for the program to run.