You can be certified in different conditions, depending upon where you live. When we certify in our area, divers are in very limited visibility using 7mm suits. In some cases, a thermocline will give you an ice cream headache if you go beneath it. Other places require a drysuit.When you know nothing, you don't know how different things are between benign warm, clear, good weather conditions and diving in more challenging waters requiring a lot more self reliance.
Being fluffed up by the OW/AOW instructors "you will be qualified to dive anywhere" gives a false sense of safety.
The course clearly says repeatedly that when you are certified, you are certified under the conditions in which you were trained. It emphasizes getting further training before diving in different conditions. Unless it has changed since I was an instructor, it is on the final exam.
You put quotation marks around "you will be qualified to dive anywhere." Whom or what were you quoting? Or were you just making it up?