Microwaves

Question

In one of your replies before Pesah you said that you boil water in the microwave not in order to kasher it but to take the hametz off the sides of the microwave. I don't understand how boiling water cleans anything off. Boling water, at least as far as I know, has always beeen understood as a kashering mechanism. I get the sense that you feel that you don't even have to boil water and just cleaning the sides off is enough, (you say as much in another answer). So why have you included anything about boiling water? Is it because it is so ingrained among people that you don't want to confuse them too much?