I am reading the Help documentation on the Variable Table
"if the open lock is displayed icon, the value cannot be edited. If the closed lock displays icon, the value can be edited."
The logic that SE is using is completely backwards to any other system, CAD or not, that uses a lock to represent the state of an object. If a lock is closed you cannot make modifications. If the lock is open you can make modifications!
Why the reversal of common practice and common sense?
I think once you use this system for a while, you'll come to appreciate it. The lock means the system can't change the value. An unlocked dimension can be changed by other geometry or by the user. To drive the dimension with a table, you have to remove the ability of other geometry to drive it, so you have to lock it. It might look strange when you look at it only in the context of the variable table, but when you see it from the point of view of the overall lock/unlock of dimensions, it makes more sense.
In SolidWorks, a "driven" dimension cannot be controlled by the user, but in Solid Edge, an unlocked dimension can be. To me this arrangement is worlds more useful. SolidWorks can't drive a driven dimension using configurations or equations, either, so in that sense, the two work the same.