They didn't completely nerf it. Steamrolling low lvl pets gives very little exp, but I'm still getting 90k+ on my 85 pally through pvp pet battles (both sides using 2 25s and a 1+).
Edit: Got the same exp as pvp battles as I did fighting a group of pets in Vale with 3 25s. My guess is they simply changed it to scale with what lvl pets you're fighting, or perhaps that was the original intention and it somehow slipped past them when implemented.