As intended for the ORIGINAL version of antique.
Originally, you could buy "antique" items from the wisp outside Trammel Despise, as part of the point system for that dungeon after its revamp.
The original version of "Antique" was that it counted time you spent in combat (how, I'm not exactly sure - it was more complicated than simply being in War mode), and after a certain amount of time of combat, the item poofed, even if in full repair. In that instance, it was obvious why you shouldn't enhance it.
However, with the full loot revamp, Antique got changed to a set of repair limits. Antique items, even if they damage easier, are now actually worth enhancing - But they left the "no enhance" code in. I believe they justified it because of some of the materials adding durability, but that was really short-sighted of them, and thinking like it was 1999, not 2014. Letting antique items be enhanced would be a drop in the bucket. Not letting them be enhanced makes them undesirable for most people.
Of course, the stupidest thing I hear are people with multiple platinum in the bank saying that "prized" items are worthless because their insurance costs. Maybe worthless for someone like me that has rarely had as much as 50 million gold in the bank, but the hyper-rich I hear making that statement could put a suit on of only prized items on, insure it, and die a thousand times without noticing the money drop.