It seems the only issue that could be justified is the unprotected fall hazard. I can't imagine you would prohibit the gate, ladder, or an opening between guards on a deck that didn't require guards. A 24" high deck with an opening between guards and a ladder provided. I can't imagine you would find authority to write that up?
So let's "think" about this, as I was asked. Let me play devil's advocate.
House over a 48" tall crawlspace. The access is in the floor and compliant in minimum size. Naturally, there are no stairs. Maybe there's a ladder, maybe not. When you lift the lid of the crawlspace access you have an unprotected fall hazard, just like when you open the gate. Shall we require guards around the opening? Shall we require a stairway, and thus a much larger opening than the minimum required? Or do we require the access lid to simply support the required live loads and leave it at that. Is this not synonymous with the fall hazard and "gate" we are discussing? Often the crawlspace access is in a closet. Someone "could" leave it open and then when I step into the dark closet I don't see the hole. Actually...I could have that opening smack in the very middle of my living room. Would you fail my inspection or require a stairway to the crawlspace?
Attic with storage. Obviously intending people to ascend into it. No compliant stairs. Maybe a ladder. Perhaps there are fold down stairs (that don't meet the code). I climb the stairs and go to the attic to get the Christmas lights. Uh-oh...I back up into the open hole. Is this not the same hazard and probability?
Hazards are everywhere. We need to be concerned with the probably hazards, not the possible. Everything is possible.
When someone makes the conscience choice to open access to an unusual feature, they are quite aware of what they are doing. If someone leaves it open...well...they could leave their stove on too? A gate serving a ladder at the edge of a deck sounds a lot like a feature meant for occasional access, not taking the burgers out to the grill on the flagstone below.
Again, the gate would need to be substantial to resist the required live loads (just like the crawlspace access door). However, is seems many are still going after the ladder as a non-compliant stairway. Ask yourself if the height of the deck would make a difference. If so...then I think the point is the fall hazard, not the ladder.
Fun stuff. I like a good discussion. Even with you hard-@sses LOL!