I've played the last few hours in Act 2 Inferno, too. Didn't feel any change, actually it seemed they had a bit less HP but that could be just different mob type champions from last time I played.
When was act 2 supposedly "nerfed" according to your friends? I entered it yesterday and killed Belial a couple of hours ago. Everything was 1 shotting me so I wouldn't notice much of a difference if there was one, I'm not sure about their HPs, but Belial took kinda long (4 people though, 1 tank, 2 semi-dps + cc and 1 real dps).
Your friends probably got better gear. Not ruling out a nerf, but I think that's the most likely answer. Gear and time spent both seem to make a HUGE difference.
Oh yeah, act 2 has DEFINITELY been nerfed. I remember the stats for average mob hit points and damage from my previous attempt at just the cavern part near the beginning.
Lacuni Huntresses used to have 90k health: now they're down to 70k. They also used to hit me for 10k, now they only hit for 5k per hit (which is still nasty, but not a third of my health)
I vote either he got an upgrade or 2, as the right upgrades can make a huge difference, or RNG. Remember mobs/champs/elites are random as well as loot, so he may have just gotten an easy playthrough by sheer luck.
Actually it seem nerfed to me as well on my Barbarian. Yesterday i was unable to solo any champion packs without kiting them, and just trying now i killed a champion pack of Lacuni Huntresses with Desecration, Arcane, Vampire and Fast affixes. It was tough but i didn't have to run around kiting them 100% of the time. I could go in hit them down 150k hp or so run out kite around till i got some cooldowns up again.
It should be mentioned i have not changed any gear.
They are still level 62 but their HP and dmg has definitely gone down. Either that or my gameplay has suddenly improved a lot over night.