Looking around in the real world, it's easy to see that humans come in all shapes and sizes. I know a tatto artist who barely tops five feet and might weigh in at 120 lbs. soaking wet. I know another one who is seven feet if he's an inch and burly. It seems to add more realism to the fantasy miniature realm if you apply that logic to other creatures as well. If every gnoll, bugbear, goblin, elf, troll, etc. were all same size clones it would be pretty boring. I have minis from Partha, Dark Sword Masterworks, Rafm, and many, many Reaper minis (but still need more). The fact that they are not all cookie cutter replicas in scale just makes them stand out more in the shadowbox. Variety is the spice of life!