And that's the point. The revenue stream is a priority. If they make a bad game just to cater to a real-money auction system, they aren't going to make any money because no one will play the game. If no one plays the game, no one will buy or sell items in the game. In order to make the in-game real-money auction system work, the game has to appeal to the masses first. Because of that, I disagree that this auction system has as much potential to ruin the game as you suggest. Will it change the game? Absolutely without question. Blizzard will be sure to monitor everything and regulate the supply of items given out by the game so the price stays high and they get more out of their percentage. Will it ruin the game? I'm pretty sure they won't let it. Again, the appeal of the game is the driver of the higher order revenue stream and they won't cut off their nose to spite their face.
I completely agree with this. Blizzard will likely not prioritize this in a way that causes the game to fail, and if they do, they will quickly reformulate it. They will likely build it in a way so as to optimize total revenue. And it may even be a boon to those all those who wish to trade items for real money who would have done so outside the system anyway (although I think this is quite a small minority of players).
I think while we mostly agree, we are looking at this from slightly different perspectives. You are saying something like, "this is an entertainment experience I am not interested in. People still interested in this [one of: are okay with the revenue model / like spending real money for in-game items / understand the play experience will be affected by in-game revenue steams]. Blizzard might as well maximize profit while still providing a generally good game experience for those people."
I'm looking at it more abstractly. While I'm not interested in this entertainment experience, I think that while Blizzard will certainly not ruin the game with this system, it is a compromise for extra revenue that will, through encouraging paying money for items and to some degree designing the economy around it, detract slightly to moderately from the playing experience of the average player. In turn, though, it will succeed in increasing revenue, and other game developers will see Blizzard's success and consider maximizing revenue over improving the play experience a desirable thing to do, thus moving games in general farther from the type of "once-you've-bought-it-it's-non-commercial" experience I would like them to be.
As I understand it, you're saying it's already a foregone conclusion that the games industry has irreversibly taken this path already, and I can understand that view. (Although maybe you should reconsider? There are lots of great games out there, albeit not as many AAA titles. Maybe give the latest Humble Indie Bundle a try? VVVVVV and Crayon Physics Deluxe are great games.)
I'm not so sure, but what I am pretty sure of is that in-game revenue streams of this type compromise general game quality, even if not to the point of ruining them. I would rather see other companies mess this type of system up than see Blizzard succeed while lulling the gaming community into accepting that this is the shape of things to come. There are still plenty of great games out there, and I don't want to see people stop making them because they can't compete revenue-wise with games that take your money at every opportunity yet are still enjoyable enough for people to keep playing them.