There's such nostalgia for Diablo2 that I think some people let it colour their expectations for Diablo3 a little bit.
Diablo2 was, hell, even is, a great game. For it's time I would even go so far as to call it a breakthrough game, but lets not lose sight of the fact that it is now 8 years later.
Designing and implementing a stable currency is not a challenge of the first magnitude any more. There is an almost uncountably large number of games on the market now that have managed the feat of a relatively stable, exchangable, player supported currency.
If Diablo3 doesn't have that, and I accept that it might not, don't be fooled into thinking that it didn't because it couldn't. It will fail to have a stable currency only if Blizzard design it that way.
When I joined these forums and saw the issue of a subscription fee was still being debated, I well knew that I would be significantly in the minority in arguing for it, but when it comes to Diablo2's trading "system", I'm fairly surprised to find any level of support for it.
With an auction house, you can find an item, post it on the auction house for your desired price and get back to playing the game, and isn't playing the game the reason we're all here, eagerly awaiting Diablo3's release?
It must also be said, that an auction house does not prevent you from continuing to make trade games, continuing to spam trade channels, if that is how you prefer to offload valuable but unwanted items. However, for those of us who, in todays days, expect such an item dependent game as Diablo always has been, to have an efficient system for buying or selling items, an auction house really is the only option.
There is much contained within Diablo1 and 2 that we'd all like to see in Diablo3, but let's keep in mind that advances in gaming concepts and computer technology make available to Diablo3 practices that weren't available to its predecessors and that those advances should be taken advantage of.