In early vanilla pets were very unique and varied and thusly hunters were varied because their choice of pet would impact their playstyle alot. The pets changed during vanilla turned them into more well-rounded but dull creatures sadly:
Fixed a bug where creatures were keeping their innate resistances after being tamed. This was unintentional and the fix will affect all existing pets.
- Source:
http://wow.gamepedia.com/Patch_1.3.0
This fixed pets such as Fire Rocs and the rare mob Snarler and was the first patch to streamline pets and make them less varied.
Base pet speed is now standardized for all pets, including legacy pets.
Pet speed can still be modified through the talent Bestial Swiftness and pet abilities such as Charge, Dash, etc.
- Source:
http://wow.gamepedia.com/Patch_1.9.0
This affected only movement speed,
attack speed standardization was implemented during burning crusade.This meant that all pets had the same speed, which nerfed alot of the fast creatures, especially the Frostwolf Howler which ran much faster than an Epic Mount, but also buffed alot of creatures who ran at speeds barely faster than non-mounted walking speed such as Tall Striders.
Overall this was a buff though, seeing as many popular pets such as the Cat Family were actually fairly slow runners without dash activated.
This change restored some variety in the hunter pets.
This caused Lupos to no longer do shadow damage with his auto attacks. Although he was never 'Overpowered' in a raidsetting because his shadow autoattacks would consume warlocks Imp. Shadowbolt effects, personally i never cared for Lupos in PvP either because he had a very slow attack speed and was only good for hitting through mana shield which was fun but rarely useful.
Bonus Info: While Lupos is a well known example there were other creatures whose attacks did spell damage. Ursol'lok the elite bear from Ashenvale did fire damage on his auto attacks, making him the official worst pet in Molten Core.