I think it’d be healthy for both the uninformed players and the economy, if those uninformed players were to hurl themselves against higher difficulties and spend their gold reserves on repairs. Then they’re faced with a similar scenario as the wow player in need of repair money: earn or buy. However you can buy gold legally in Diablo 3, if you so choose.
Looking at the problem from another angle – gold selling is still in rude health in World of Warcraft (I’ve not heard anything different) in spite of attempts to remove the hackers and farmers who acquire that gold; in spite of the inflation caused by 3 (soon 4) expansions; in spite of access to add ons that pretty much earn gold for you on the auction house; and in spite of the player base having 6 years to get to grips with a (arguably) simple, single currency economy. There’s still a demand for gold. Of course, the amount you can now get for $5/£5 is now greater than vanilla.
This is the type of inflation Diablo 3 will suffer from – it’s an inflation that can’t be avoided. Expansions bring the need for more challenges and therefore more rewards. More rewards come in the form of better items and more gold. More gold entering the economy is inflation.
Hyperinflation (or as close to that as you can get in a digital economy) is what would be more troublesome. This would be characterised (for example) by a Keen Wand of the Hawk being 700 gold at launch then climbing (as gold loses value/players gather large fortunes of gold) to 70,000 gold.
But I am not convinced Diablo 3 gold will devalue to the point where it’s worthless. As I mentioned above, Blizzard have the tools to counteract this. They control how much gold enters the economy. Totally. Players can farm and actively pursue gold but they’re simply ‘mining’ it out of Sanctuary. Farming it. Blizzard are omnipotent. They set the amount of the resource that exists in the world. The amount you can gain in total and the amount that is required (through gold sinks) to keep playing the game in the manner you like