The phenomenon discussed in the article (the surprising lack of any de-facto currency arising in TF2's barter economy) is very interesting, because the economy in Diablo 2 did develop its own currency around a single item -- the Stone of Jordan (SoJ).
D2's economy was very similar in that it was almost purely barter-based and players had limited inventory space to store their items. SoJs occupied the smallest possible amount of space in the inventory (1 square). They also had high intrinsic value, as they were not only powerful items but also ingredients in two important crafting recipes.
Interestingly, SoJs lost their currency status once their intrinsic value depreciated [1]. A new mechanic, runes, was introduced, and they became the new currency. However, to my knowledge no single rune type rose to dominate the others and claim true currency status, so the current market is a bit more muddled.
TF2 does have somewhat de-facto items serving as currency, although none of them offer any specific gameplay advantage. They are:
* buds (limited apple Earbuds given for a short period of time): These are worth roughly 2 bill's + some keys, or 24 keys.
* bill's (Bill's Hat, also given for a short period of time for those that preoredered left 4 dead 2) worth around 8 - 10 keys
* keys worth around 2.44 to 2.55 metal
* metal
Everything else is measured around these 4 items. All these prices seem to come from a single source. The "TF2 Spreadsheet", a google docs spreadsheet, created by "the powers that be" which seem to have defined these prices somehow.
It is not a perfect system though, because what generally happens is the values are used as a starting point for a sale. Whoever's selling wants more, declaring that the spreadsheet prices are only a reference, and they know their item sells for more. Whoever's buying usually ridicules the seller saying that the particular item will never sell for the spreadsheet price, which is already outdated.
How trades are made with this system, I don't understand. For those not wanting to deal with all the chaos, there's http://www.tf2wh.com/, which seems to have a rigid credit currency set. Of course it helps that most of the trades are done by bots, so no human interaction is required.
D2's economy was very similar in that it was almost purely barter-based and players had limited inventory space to store their items. SoJs occupied the smallest possible amount of space in the inventory (1 square). They also had high intrinsic value, as they were not only powerful items but also ingredients in two important crafting recipes.
Interestingly, SoJs lost their currency status once their intrinsic value depreciated [1]. A new mechanic, runes, was introduced, and they became the new currency. However, to my knowledge no single rune type rose to dominate the others and claim true currency status, so the current market is a bit more muddled.
[1] http://www.diablowiki.com/The_Stone_of_Jordan