What missed in the discussion of laptop locks is the realization that (a) you'll never prevent a determined thief from defeating the security lock, and (b) if you deter the casual / opportunistic thief then you've achieved your purpose.
So yes, Resist, you're perfectly correct. Even a well built cable lock is easily and quickly defeated by the knowledgeable and prepared thief. If he or she is determined to take your laptop, it's gone. The very best solution is to take the laptop with you or lock it in a desk drawer.
Since that's not realistic in an office (or dorm) environment every time you step away from your desk, then the next best thing is create a deterrent to the majority of potential thieves who are likely neither knowledgeable or prepared. Thus using a cable is better than no cable; not necessarily because it creates a significant amount of additional security, but because it serves as a deterrent to the majority of potential thieves.
