Because a gryphon is a mix between an eagle head/wings and a lion body. That's the definition of a gryphon and Blizzard is calling them gryphons and they looked like that since Warcraft 1. Now they changed it without good reason.
I did not complain about extra polygons, I complain about the art-direction. It contradicts all previouse Artworks (including painted ones without any polygonal restrictions) and it looks wrong on many levels.I think it looks great.. plenty more HD.