I agree, they kind of do, but they are solid stainless steel, not tubes. These are definitely meant to take some pretty serious load and are backed with 1/4" SS backer plates. About the only things that are more solid are the mast and winches. My initial inclination was that they were some sort of bollard, but they have that groove that clearly has some purpose. And, the groove has crisp edges and I would expect anything meant for line-handling to have rounded edges.
Also, notice that they are mounted on wood blocks to bring the bottom flush with the toe rail. That seems intentional and suggests either line handling (via the nearby chock, perhaps). Or, it means that whatever attached to it needed to clear the toe rail.