[jasonkester]

It's a log scale, just not necessarily log10.

It's like lots of things in sport, actually. Imagine the progression from running a 6 minute mile to a 5 minute mile to a 4 minute mile. Now go to a 3:55 from there. It's a much smaller notch than 6:00 to 5:00, but will take you ten years of training.

So sure, you can consider it just adding more weight to the bar in a linear fashion. It still a lot harder to lift each individual pound as the weight increases.

[justinator]

Actually, I don't consider it like adding weight, since climbing grade difficulty isn't calculated in a way that would be so simple.

There's no objective way climbs are organized in difficulty except by subjective feeling. Holds may be (say) smaller, and/or farther apart, but the difficulty can only be sussed out in a general sense - there's far too many things to take into consideration.

Compounding all this is that a climb could be more/less difficult because of a climber's body type (tall/short climbers excel at different climbs)

So you're left with a consensus, which is living and breathing, not a calculation.