Because one is real, which is my point.
I'd be interested in your definition of a 'real' currency.
Fair enough, but that doesn't really change my point, which is in the paragraph you chose not to quote.
Ok sorry (I believe this is your point)
I'm not saying that gold and only gold has no value. I'm saying that that what the gold represents has no value itself. Thusly the items you can buy with it. IRL, this is not true. Sure, we agree upon the value of money, but the point is that with that money I can buy things that are not simply "up for grabs" and created out of nothing. If something can be created out of nothing, the value of that thing (and thus the value of money) is severely reduced.
I believe if the players themselves could create the items (and the amount they could create was not time restricted or resource restricted in anyway) this would be true. Value of things that have no variable cost (i.e. can be mass produced for nothing) relies solely on supply restriction, and this is the same reason that software carries a value. For instance a software company restricts supply by setting a price for its products, which is different to products that carry a variable cost that would be produced where marginal costs equals average cost(and price will be set according to demand.) So as there is a limited supply of the items they have an attached value (WoW currency or US currency.)
As I also don't play WoW I am unsure about this next issue. If the items you can buy with in game gold cannot be traded it can substantially devalue them and the currency but I don't believe this is the case. Also as Blizzard does not let people sell their in game gold, it does decrease the value of the WoW currency, but allows them stricter control over the circulation of the gold.
To address another issue, of course a bot can run without player guidence and this certainly reduces the value of the currency, but it still takes time. Since you cannot make infinite amounts of gold in an instance the currency still has value.