AH was and is one of the best features ever made. Why?
Look at PoE, like Shinzai said, ppl have to spam trade chat, forums and yet are not fingind buyers. Why? It is very simple. Buyers won't read this crazy trade chat. Buyers won't read +100 threads on the forums. Actually this is very funny, to see all those hardcores trying to sell gear and like I said in the past...soon or later nobody will buy these items, market will be flooded. Only very rare rolls will sell, as casuals are tired of this product or simply don't have time to read this spam-trade-chat and forums nor they know about one website that has nice forum-search option for items.
What makes successfull trade?
Accessability and comfort of search. Trust me, +90% of players are lazy, D3's search options are like a miracle for them (and for me too). Without it, I think that the number of items being sold would be 100 or even more, times smaller.
Also keep in mind that: D3 doesn't have runes. There is almost no alternative currency.
And why the market is flooded in D3, again?
It is very simple: proportion of items produced by hardcore players is way beyond needs of all (mostly casual) players. Look at the WoW and it's itemization, almost every item is BoP or BoE, tradable, usable end-game items are like 10% of all. Market is stable. The same goes for crafting.
D3 should have BoE or at least BoA itemization. This would help somehow.
Another problem, connected with that, is disproportion of hardcore findings vs casual findings. Compare MP10 infreno+Paragon 100+tons of MF dude vs casual struggling to farm MP1. In theory, the first guy may produce 10 times more items than that casual.
Conclusion: think by yourself, do not read mindless cries and shouts, almost every person spaming and yelling "rmah, ah destroyed D3!" have never seriously considered what I wrote and has never seriously thought about the system. That's it.