In reference to "Architecture" To say that there are two types of Gargoyles is wrong. Gargoyles are only ever water spouts. Those that look like Gargoyles that are statues placed to guard or ward off evil spirits are called Grotesques. so the majority of 'Gargoyles' at hogwarts are actually incorrectly named.
Of course as there seem to be living creatures called Gargoyles in the wizarding world, this accounts for some of them.