choda_boy, Why? Because thugs in UK/Canada know that chances of bumping into a person with the real gun are slim to none. Also they know that gas station clerk will give them money 9 out of 10 times when threatened with a replica.
I've seen many people who got robbed by a teenager with "a gun". None of them were brave enough to try anything except for giving up the money. Most of people will not test their luck when it comes to "your life VS contents of you wallet". That's what thugs use all the time. Fear of being shot.