Of course not. The longer stick will allow the player more leverage, making it easier to bend the stick.
It makes sense as a standardize way to describe a property of a specific material. It's similar to how meat is sold in dollars per pound or how some things are sold by the square foot. I agree that there's probably a better way to go about things with the public, but the cynic in me thinks there's other advantages to keeping things the same or at least obscured. They can now make sticks shorter, saving themselves money in the manufacturing process, but still present the facade of the sticks still being the same. And the public generally won't notice. What they will notice is not being able to find sticks with their preferred "bendy-rating."
They say the flex rating doesn't change because it's a property of the material. They say the leverage changes as the length changes, and the change in leverage makes a stick easier or harder to bend.