An auction is when you bid for somthing, if they add a feature to buy from the wards interface its still not an auction house, anywhere that uses the term auction house for a buy now feature either doesnt know what an acuction house is or just uses the term because everywhere else does.
If they add a buy now feature to the wards interface its still the wards, have you ever seen an rl auction house that lets you buy now? ebay doesnt count because it has bidding, just has an option to buy now if the seller wants it.
Bidding is what makes an auction house an auction house, if they just have a buy now button its still a market just without the need to run to the retainer.
Edit:
http://dictionary.reference.com/browse/auction