Take this into consideration.
Maybe Blizzard doesn't want you to have really low health pools.
Maybe Blizzard is trying to fix the issue.
Maybe said fix involves reducing the damage taken to 35% but only if the damage taken isn't more than your maximum health pool.
Let's say above changes are true.
Let's also say I have 35k HP.
Now let's say you take a "Hard" hit for 10,000 damage. Easily mitigated with 35,000 HP.
Now let's do some math.
35% of 35,000 HP is 12250. Since 12250 HP since the 10,000 damage hit is less than 35% the rune doesn't work and you take 10,000 damage.
Let's say the hit is instead 20,000 damage. The damage taken will only be 12250.
Sounds pretty much like how it works now right?
Well let's say you had 5k HP.
35% of 5,000 is 1750. So with a 10,000 Hit you should only take 1750 right?
Well, if the change is to only negate the damage if you could have survived it in the first place then you will take 10,000 damage and die.
Sounds like a better use of the mechanic IMO.
Lets say mobs in inferno hit for 58k, because they do, in Act 4.
If that's true then the problem lies with the tuning of the content. Either that or you just haven't seen enough gear to get you to 100k Life or more... It's probably just because you don't have the gear. But what am I saying, that's a terrible idea.
Seriously go look at the AH and search for items with 200 or more vitality on them. You'll find quite a few.
Hell, even if you had all 13 slots decked out with a minimum of 150 (I checked the AH. They exist.) you're looking at 78,234 life. That's not taking into account that there's items with even more vitality than that on them, some even reaching upwards of 230 or more.
So let's look at the math.
If you equipped all 13 slots with at least 150 vitality you're looking at 150 * 13 = 1950. Since each point of life gives you 34 vitality that would be 66300 life. That's more than 58k meaning force armor would be useful at that point.
So let's take this even further... Let's give yourself a helm with a gem socket. Now let's slap a Radiant Star Amethyst in there. That's an extra 18% life.
So if I take 66300 * 1.18 I get 78234 for a low end health pool.
Now let's say my average vitality is more like 200 per item.
That's 200 * 13 * 34 = 88400 health without a gem and 88400 * 1.18 = 104312 Vitality with a gem.
Don't believe me? Look at the AH and search by vitality with a minimum rating of 150. I assure you that you will find AT LEAST one item with that much health on it. Now considering these are all Blues and Yellows and not Oranges the Legendary items will probably have even more.
Seriously, take the time to think about it. Vitality is the way to go in inferno end game.