Maybe so, but in principle, it's not that different. It's very different. Irradiation uses ionizing radiation that destroys the DNA of living organizms, thus killing them, but does not heat or "cook" the product being irradiated. Microwaving food simply heats the product, often in irregular patterns (which is why many have added the turntable do-hickeys). As a result, areas that do not get heated enough to kill bacteria can still be contaminated. I've read that any organizms smaller than the wavelenth of the microwaves (About 3 millimeters, the size of a small ant) are not affected by them.