The "Real Money Auction House" is entirely new, and I'm not aware of any other game enabling such transactions at a player-player level. You can sell/buy stuff for gold, but with RMAH, you can do it with real money. In all reality, the market settles at a gold/money conversion rate. In North America three days ago, that was at about $1/100,000 gold.

It's not heavily based on RMAH, but if you want to progress quickly, you spend money. I don't think it's a pivotal part of the economy at all. I think it's more to make sure Blizzard gets a cut of gold sellers/buyers.