However, they are very good at refinement. Which is one reason why competing too directly with them never works - if your ideas are compatible with their own, they'll take them, refine them, and put them in their own game.
You hit the mark right there. Refinement.
One thing that I did not mention in the OP is that Blizzard took steps back when they realized their original business model simply did not work and alienated a huge section of the playerbase. They launched Auction House and then removed it. May be their approach was too drastic to completely eliminate trade from the game, but, from certain perspectives, it makes sense - What you find is yours and you can share it with others who took part in your adventure. It does put certain restrictions, but, overall, I like it from philosophical standpoint.
I wish ANET looked back at their mistakes/failed implementations and said, "Hey, we ♥♥♥♥ed up but, we will fix it." Hopefully, they will.