Thats the worst argument possible.
By that logic, everyone assumes all unarmed citizens are armed. Police and military are assumed to be armed. There is no concealment or blending in when there is no choice in the matter.
And most off duty cops do carry concealed... last I checked.
Oh, and your absolutely correct, petty theft happens more often. That's akin to saying, fender benders happen more often then fatal car accidents, so don't worry about wearing your seat belt as it PROBABLY won't happen.
And, your right, someone would PROBABLY overlook an open carry, if they were PROBABLY in a hurry. For that matter, if they are PROBABLY going to overlook it, exactly how the hell does it deter crime in the first place? You can't have your cake and eat it too.
Personally, I don't like to risk my personal safety on "PROBABLY". but, thats a difference of opinion.
Another factor you will see with a lot of concealed carry folk is they don't like other people - gun owners included - to know they carry, or where they carry, or often, what they carry. They want the information on how they will defend themselves, or if they will defend themselves, to be cutoff from the world, in the unlikely (but possible) event, someone is ever bent on coming after them. If you always open carry a 45 on your left side in a black holster on your belt, everyone in your life is going to know it. Typically, strangers don't kill strangers, and if someone is pissed off enough to come after you (not to steal your watch) they are going to have the advance intel to know exactly what your reaction would be. Will that prevent them from acting? maybe. Will that limit your options if it doesn't?

You really won't have any.
The problem with open carry, is not that it will deter some crime.. sure it will. It's what happens if it doesn't? You can't be naive enough to think having a gun on your belt will deter 100% of people out there. In the event someone notices it before hand, and it does not deter them (cause and effect) your a goner. Unless your Psychic and know what everybody is going to do, concealed or open carry is always REACTIVE. You can't act until a thread has become apparent, and in this event, that threat will not have become apparent until it (possibly) kills you.
Also, the difference between me and the guy who wrote the original article? I don't place bets on what will or won't happen. Fact of the matter is, whatever happens will always catch you off guard, and you can't predict it. There are millions of potential situations that can happen. Only a small fraction fit in with the OP's article-writer's intention. Almost none will you have any mental preparation or advanced warning.
That grocery store example? That happened. this city, about ten years ago. Two unarmed men tried to stop him, he shot both before they even had a chance. Then his girlfriend. Then himself. Weak example? It's called LIFE. Would he have noticed an open carry? I won't guess either way, the possibility exists. He didn't come in guns blazing. He caught the entire store off guard. I do know he would not have been deterred by one (and that a concealed carry, or an unnoticed open carry, would both have had the chance to stop him, and save 3 lives that day)
The original article has been written with the mindset that EVERYTHING can be deterred with open carry. That by carrying openly, a person will NEVER have to use it. Can you not see the flawed logic?
When it all comes down to it, it's a matter of personal opinion. I'm not saying you should not open carry. That's your right and your choice. I'm saying the O.Post has a very limited perspective on the situation and doesn't represent the full picture, and both sides of the issue.