Q u o t e: I have a question related to this--Is it even legal under the ToU of Battle.net and/or the game's EULA to sell in-game gold of Diablo II for real-world cash?
Yes, it against the ToU of Battle.net to sell any in-game items for real worl cash. However, they are working around a loophole. They are not selling in-game items (or gold) for real world cash. They are selling FORUM GOLD (as a medium or currency) in which you can use this forum gold to trade for in-game items. So you are not paying for items directly. You are paying for FORUM GOLD which allows you to pay for items indirectly. Also, not everyone that uses forum gold pays real-world cash. It is possible to generate forum gold simply by trading your items for it. It's basically a virtual currency.
Also, it is worth noting that the Diablo II Stores that are spammed in battle.net channel/games constantly are also using a loophole. They are not selling these items for real world cash either. They are collecting a "finder's fee" for the item that they will "GIVE" you in return. This way you aren't paying for the item directly, but instead you are paying the store for finding the item for you.
Get it? It's basically a bunch of scumbags that know how to work around the system.