It's all about gear. Dudes like Kripp are just insanely geared so it looks easy.
Hate to break it to you bro but % life steal is reduced by 80% in Inferno (i.e. if you have 1% life steal, in Inferno you're actually only healing for .2% of damage done). What you want is + life per hit.
Started working through act 1 earlier today, my barb isnt the best geared in the world 35k health with 9k dps and 9% damage to life with part of most of my skills being ones that give life back including the ever useful ignore pain with 20% damage to life rune, im finding certain rare mob combos mobs very difficult but others are no problem, i have a buddy who is a witch doctor who has similar issues but with different combinations.