Retention is not required in Wichita, or Kansas. Somebody was just inserting their opinions into the law.
I occasionally carry one of my handguns without retention, but the holster is angled and fitted to make it difficult to draw except by the wearer. A back-up, a easily accessible knife or some other kind of plan is a good idea if not using retention.
In my opinion retention on a holster is a false safety anyways. If somebody is trying to grab my firearm, my first reaction will be to force it down in the holster and not allow its removal weather or not a retention feature is in place. Second, I go for the back up weapon.