That's not why he comes He comes because you have trained him to respond to the tone as a come command, and that command is more powerful than your voice because it has been consistently re-enforced. You may not have done it on purpose, but that's what you've done.
If you yelled come and re-enforced it more consistently, he would come when you called him. Think about it... You yell come and nothing happens (necessarily). You hit the button and there is re-enforcement, each and every time...
As it is skip the verbal and just hit the button
Nothing wrong with it BTW, just trying to get people to think more clearly about what they are doing and why the reacts the way it does.