I think D3's AH failing was using real money, not just balancing or buying gear by default.
Buying gear in WoW is easy and a given up to a point, but limited to in-game currency. To buy some of the best gear, you just have to be the owner of enough gold to buy something from one of the two auction houses if it shows up. That meant you were active in your server's economy (helpful) or you were buying gold from scammers (which a lot of people are scared to do) - or you were raiding at a point where that gear was equivalent to what you can get, so you just ignored it (a small minority of raiders, not just WoW players overall). If real money was involved, it'd probably turn into something worse than D3's AH fiasco where people would quit playing since everyone playing for non-RP/solo reasons would eventually be forced to spend a bunch of money on top of in-game time to be on an even footing.
Not that I think D3 should have followed the same exact footsteps as WoW in terms of how to make money, but I'm looking forward to next month to maybe get around to start playing D3 again now that the AH will be gone there.
Most gear in WoW cannot be traded. If you want to buy the best gear, you wait for a guild to farm the content, then buy the gear from the guild by doing the instance with them. People do trade real money for this service, but it is understandably quite expensive.
Current-tier raid and PVP gear can show up on the Black Market Auction House, sold by NPCs. The BMAH sells a very small number of pieces during the few months it takes people to clear content. When I played in a top 20 US 25 man guild in T14-15, our BMAH was usually camped by the other faction, so we couldn't buy stuff anyway. It didn't make any noticeable difference.
Buying gear in WoW is easy and a given up to a point, but limited to in-game currency. To buy some of the best gear, you just have to be the owner of enough gold to buy something from one of the two auction houses if it shows up. That meant you were active in your server's economy (helpful) or you were buying gold from scammers (which a lot of people are scared to do) - or you were raiding at a point where that gear was equivalent to what you can get, so you just ignored it (a small minority of raiders, not just WoW players overall). If real money was involved, it'd probably turn into something worse than D3's AH fiasco where people would quit playing since everyone playing for non-RP/solo reasons would eventually be forced to spend a bunch of money on top of in-game time to be on an even footing.
Not that I think D3 should have followed the same exact footsteps as WoW in terms of how to make money, but I'm looking forward to next month to maybe get around to start playing D3 again now that the AH will be gone there.