The problem with real world value of in-game items is who is held liable should anything get stolen. If you condone it or actively promote it, then surely there's some liablity if people steal or lose things due to a failure of in-game mechanisms. You can't put a get out clause in the T&Cs and hope that covers it.
Some games companies say they don't allow real world trade of game items and money and attempt to police it in varying measures. Blizzard claim to do so, but a quick check of eBay indicates otherwise.
Most games companies seem to nominally say they don't allow real world trade but turn a blind eye to it, the Mythic approach.
Then there's those like CCP who don't seem to mention it in their T&Cs at all and operate a total hands off approach. Whilst this seems ok for EVE such an approach won't work with games with a less 'anything goes' theme.
In the future we may see games which actively encourage trade and even sell official game upgrades for cash. This takes things to another level. The impact on gaming will depend on if the official bought upgrades are merely fluff (fluffy dice for you in-game car) or meaningful (a turbo charger for your in-game car). And then the whole liability can of worms is opened.
If a games company promotes the concept that in-game items have real world value, then if any theft or loss is due to game flaws or bugs there's a real world lawsuit inbound. And how do you deal with virtual theft when it happens within the games allowable mechanisms? This has to be policed in some way, not all games have an allowable piracy theme. If you're actively condoning/promoting real world trade then an incident like the Guiding Hand one in EVE takes on a very different perspective. As I say, a can of worms.
Personally I don't have a problem with in-game items having real world value as long as the game experience of regular players isn't affected by it. I don't mind if someone who can't play 24/7 wants to spend a bit of their hard earned cash to buy some in-game gold to speed things along (bit like Las's decorators). The trouble comes because in most games it does impact the player experience and tends to lead to farming, camping and looting issues. MMORPGs of the future have to address this as game items are always going to get sold in the real world, like it or not. Games need better mechanisms for handling it.