That said, actually determining the price of an item in FFXIV is more time-consuming and inefficient than in other games, so I'm sure some people don't bother with it.
The people playing now probably check, but in a retainer system like this (if the game ever gets semi-popular) most
won't. It just takes too long just to properly price something.
Markup does happen. A Dia II scroll in FFXI sells for 10,000 from an NPC, but goes for double on the AH. Is that wrong, no of course not, but in a game like FFXIV you'll have prices for a similar object go for 15,000 to 50,000 because 1. People don't know an NPC has it and 2. People aren't going to check all the retainers to get the best price.
What then happens is that people won't pay the 50,000 gil for the scroll. So the seller vendors it or lowers the price. Eventually the price will come down to it's equilibrium albeit at a much slower rate in comparison to say an AH
That is precisely the reason why I was against the wards in the first place because they were just a slower form of what we've had before.
Now if the wards actually utilized the retainers through a more complex UI (actual AI bartering between retainers, on the fly price changes based off of demand, leveling up of retainers (or achievements) through things like marking items up) then I could see the reasoning behind it.
Otherwise it's just a boring timesink.
EDIT: (I didn't know about the 20 lowest prices thing) But as I've argued before if they include every single (crippled) function of an AH without it being one, what's the point?