What is really SILLY here is that the researchers failed to realize they aren't killing bacteria, viruses and parasites with the MICROWAVE. If you wet a sponge and cook it for two minutes in a microwave, you're going to bring the water in the sponge to a BOIL.....
I heat my tea or coffee in a large ceramic mug in the microwave for two minutes and it comes to JUST boiling. I imagine that a significantly less amount of of fluid inside the sponge would come quickly to boiling point and remain so for a good minute.
So... the EASY solution is to boil water on your stove, put your sponges in there and let them boil for a couple minutes, and this would accomplish the exact same thing. Without using MICROWAVEs.
Good grief.
(Oh, and if you put them the little silverware holder in the dishwasher, you do the same thing... duh)
I suspect the both the direct and indirect (water heating) effect of the microwaves helps to kill the germs. After all you can cook meat in there, and meat is made of cells, just like the germs are.
But I don't think filling a pan with waters, waiting for it to boil, and then having to clean the thing, is EASY, compared to wetting the sponge, throwing it in the microwave and pressing a couple of buttons. YMMV.