The following is cut and pasted directly from the 2005 Fox Forx manual. I'm not making this stuff up! A F100X may well feel rigid to you, coming off a non Terralogic fork. I owned one and I know that it is not supposed to feel completely rigid.
"F80X and F100X Damper Operation
FOX FORX F80X & F100X with TerraLogic Technology represent the ultimate in cross country front suspension. The F80X and F100X feature a lock-out that is controlled by an inertia valve. The F80X and F100X remain locked out until there is input from the trail. The inertia valve then opens allowing the damper and subsequently the fork to function normally. When there is no longer input from the trail, the inertia valve closes and the fork again locks out. The lock-out featured on the F80X and F100X is firm but not rock solid. This is an important design characteristic and is normal. Featured adjustments on the F80X and F100X are Rebound and Bump Threshold."
Ronnie.