Aren't you essentially buying gold for $3 a month??
No you are buying the added functionality and ability to access your favorite form of PvP from locations other than your PC. What you do with the access and functionality is entirely up to you. If you were to only buy goods at overinflated prices you would in fact be paying $3 to lose money.
Isn't this a case of the rich getting richer??
If this is meant to apply to Blizzard/Activision sucking more money out of players much the way they do by allowing you to buy mounts and mini pets then yes. If you mean players with a lot of gold having the ability to make more gold then no. Without opening a socioeconomic can of worms I will generalize (possibly getting my knuckles rapped in the process) and state that the highest real life income earners who play WoW are not the same individuals who play WoW 18 hrs a day.