It seem like Blizzard condones buying wow gold if they sell it themselves.
It runs the risk of encouraging hyper-inflation on servers. WOW Gold is already pretty cheap, consequence (I suspect) of hackers' increasingly sophisticated means of parting players from their accounts. Blizzard running the prices down to drive gold-sellers out of business would be the definition of a Pyrrhic victory. The more inexpensive that wow gold gets, the more that buying it becomes a rational choice over spending the time to farm it in-game or taking the risk of playing the auction house -- and the closer we edge to the situation on the beta servers. Then people who already buy wow gold against the terms of use will continue to do so from gold-sellers, because the only selling point to "Blizzard gold" would be that it's legal -- and that's not a sufficient incentive for people already comfortable with ignoring the rules. Moreover, for newer players it would have the unfortunate effect of making it seem like Blizzard condones buying wow gold if they sell it themselves.