As I said,

>> Embedded stuff varies, but frequently anything capable of running a general purpose OS (which IMHO is generally the line to call it a "computer") can have it replaced.

A microwave isn't generally viewed as a computer. In particular, if not even the manufacturer isn't running arbitrary code on it (only a tiny little program to do... microwave stuff...) then I view it as out of scope to an argument about artificially-restricted computers.