Wolverine heals from shots from Hulk and Spider-man so quickly because the organs are still there. It's like knocking down a Lego house. You still have all the pieces there to put back together. Now, if you do something like burn away his flesh, rip out some organs, etc. it takes him much longer to heal because his body has to start from scratch. Personally, I don't believe he should be able to replace organs and the such, because your body simply doesn't have the resources to grow and form new organs. Your body can rebuild skin, hair, teeth, organ tissue, etc. but the actual organs themselves are a different story. Your body can patch job just about anything, but how is it going to make a whole new ****ing liver? It can just build it piece by piece, it has to make it the only way it knows how, by growing one from scratch, which takes a hella lotta time and a hella lotta energy and resources. Thus, if you ripped out all of Wolverine's respiratory system, he'd die. His body can't reform them in time to save himself, whilst his digestive system he will live as long as his body can provide enough resources to rebuild this system, because it's not required immediately to live.