Not when it comes down to choice ... you don't have to play the game, you don't have to use the auction house. 

I'm sure that Bizzard didn't make the market to 'exploit' someone, more likely they understand that some players like a market base mechanism to sell items. They are just catering for users. 

Played the game for around 10hrs, it's not that good and I can't see myself going back to it. At least Path of Exile has very good game mechanics, now if only I can find some more Exalted Orbs ...

One game off the top of my head that was:  Street Fighter X Tekken

Do you consider McDonald's and Wal-Mart unethical?  How about casinos or the Stock Markets?

Whether ethical misconduct requires intent is a philosophical matter, and I do love those, but suffice to say there is at least one camp that considers intent irrelevent (consequentialists/utilitarians). I don't think it is an important issue here though.

I think a design can be unethical, let's say if we saw stadium plans that had extra concession stands where fire exits should be. Maybe the designer forgot about them and there is no intent to endanger people. It is a matter of language and convenience to me. Game designs of multi-million or billion dollar games tend to be diffuse, so focusing on the object seems appropriate. In this case the purpose or effect of the design (depending on what you want to focus on) is to trigger reward mechanisms in some players to engage in shallow, compulsive behavior for hundreds of hours and even spend considerable sums of money to get the effect of hundreds of hours of grinding.

I think casinos are unethical, in that they bring more harm to the community than good they produce. Stock markets are a mixed bag, but there are practices which are legal but have the same effect of enriching few at the expense of a great many (like the practices that led to the recession). 

I think games can be enriching activities and I don't think it is wrong if they are designed to be a good way to waste time. I think it crosses the line when they exploit vulnerable people for gain, like casinos do. I see this kind of design in the App market on the Ipad a lot. There will be a game, often free to play, which will try to stoke desire for in-game resources, to the point it is not playable without them. Then they will have in-app purchases which range from a few dollars to a hundred dollars for in-game resources (all repeatable). Are they trying to get fair value for their game, or are they trying to exploit people with addictive tendencies to bleed them?

People are responsible for their own behavior.  If blizzard is honest with their system, the numbers add up, then there is nothing wrong with it.  Don't like it, don't use it.