all microwaves do is makes the molecules and such vibrate, which causes heat, and the wavelengths are designed for those of water so it heats more evenly and stays warmer longer, which is why everything comes out of the microwave steaming, hot water.

Water can only boil at 100C no higher so the water may only be as hot as 100C but the steam could be hotter, so its still a mystery at how hot a microwave can get.