Maybe I missed it, but why isn't wheel weight included in this discussion? The weight of the wheels has a much larger effect on climbing than the weight of the bike/rider as a whole.

That being said, there are several factors that play into this. Crank and chain ring flex, mechanical drag in your drive train, frame stiffness, the stiffness of your shoes, etc. It all matters. To say that all of those factors are just marketing bs is foolish.

Also, I'm not even sure that I agree with those that say 1 lbs. off the belly is the same as 1 lbs. off the bike. When you climb (accelerate) a bike you are pretty much pushing down on the pedals and the bike wants to move forward. As the bike starts to move forward you have to hold onto the handlebars and "pull" yourself forward with the bike. I think the weight of the bike matters because it takes up energy as you manipulate it. This energy is used at a different rate than it would be if it was attached to your body.

I don't know if that makes any sense, but the point is that certain bikes are definitely better climbers than others. If all bikes were the same and weight didn't matter then we wouldn't be where we are today in terms of technology.