What's more, there's nothing up in Inferno to even really motivate people to seek the higher gear. They're not striving for that impossible amount of experience or skill points anymore, trying to perfect their build. The legendaries are a joke (and probably will remain so even after rebalancing.) That leaves set pieces or hoping the generator spits out a "perfect" rare item. At which point you're done playing anyways.
I just don't see who is going to be playing Inferno obsessively to get items except the people who want to turn them into a profit. It's going to be tons of supply with next to zero demand as far as the auction house goes.
So yeah, I agree. Time will tell but I expect D3's long-term appeal to be one of the biggest Blizzard flops ever, unless they put out an expansion that is basically a 2nd game to make use of that gear. The content of D3 already feels old, and that's after 2.5 playthroughs. With the 4th Act feeling more like Act 3.5, you don't even really get the ZOMG SO INSANE enjoyment that you once got doing Act 4 highest difficulty in Diablo 2. Act 3 seems like a far better place to kick ass and chew bubblegum.
Maybe they're banking on PvP and the eventual e-sport arenas to be the real driver of AH profit.