There are two schools of thought as to how to deal with a robbery. One is to just give them the money and they'll go away without harming anyone. That's most likely the basis for the company policy. In this situation however, it didn't look like passivity was going to work. The robbers didn't leave and would, in all likelihood, have killed him anyway. And that led to the second school of thought, which is violent resistance.
The real problem with the company policy is that's like giving an open invitation to any would-be robbers. If employees were empowered to exercise their judgement and use resistance and self-defence where possible then maybe there'll be fewer robbery attempts.