Blizzard are planning on implementing some changes to the pets in Diablo III, and have detailed some of the changes they're planning on making in a recent post on the Diablo forums. The main thrust of it is that they're going to make pets toughness more scaleable, so they'll be able to take damage in-line with their owner.
Blizzard's John Yang explained: "Pets should scale with your survivability stats. They currently scale with most of your stats but not all of them. This is being worked on. Pets should derive their Toughness from yours, and if you skip out on it, your pets' survivability should be noticeably lower as a result. On the flip side, they should be noticeably tougher if you've increased your own Toughness. You shouldn't skimp on Toughness just because you have pets."
"We don't want pets to be invulnerable tanks. In the live environment pets are too squishy, but even after our review is done in a future patch, if your pets are still dying a lot, we want you to be looking to increase your Toughness, which will consequently increase your pets' survivability."
The plan seems to be adjusting the amount of damage done by incoming attacks, by factoring in how likely it would be for a player to avoid an attack. There'll soon be three different categories to inform how the pets are affected by a connecting attack.
Full damage to pets - Basic melee/weak projectile attacks, not expected to be always avoided by a player.
Reduced damage to pets - Special attacks such as fireballs, which typically deal more damage than a basic attack, are pretty bright and visible, and can sometimes be avoided by the player. Good example are Perdition's volley attack or Agnidox's fireballs.
Drastically reduced damage to pets - Persistent AoEs for which the player is intended to move out of quickly or highly-telegraphed attacks for which the player is intended to avoid altogether. Examples are Thunderstorm monster affix, Mallet Lord's arm attack, or Morlu meteors.
These tweaks will have the most impact on players who use the Witch Doctor class, although there are other examples that'll benefit. Any abilities that don't fit into the solution as outlined above will be addressed in a future patch.