Worming is something that has to be evaluated by the individual . . . 
Were there chickens on the property before ? ?
Are there wild birds with access to your flock - - fly over head and leave deposits in run ? ?
Are your birds on the ground or in cages with no access to ground ? ?
Do your birds free range and eat things like grasshoppers, worms, etc.
All of these effect the likelihood of worms in the chickens.
I do not live too far from dawg53 and I worm my birds 2 times a year.  
There have never been birds on my property before.  
My birds free range during the day time and are in a covered run and coop at night.
In the south,  we have a humid, wet, bug infested growing climate almost year around.  We see very few freezes.
Commercial chicken houses do not worm their birds because they never touch the ground,  have access to bugs, worms, grasshoppers,  or have wild bird visitors.  So, the probability that a commercial chicken will get worms is slim. . . .