_Unlike someone said, it doesn't benefit sellers, because being able to see what price people put their stuff for, its easy to undercut, leading to low prices. Price history is more interesting in that case (even if it has downsides like XXXX item stays at the same price cause everyone puts it for this much).
Actually both the wards and an AH are pretty much on the same ground for undercutting. Yes market wards show the exact price whereas the AH was a bit of a mystery, however at the same time people undercutted since the lower price always took priority on what sold first.