blizzard doesnt even have a good micro-transaction shop on a monthly sub game..
Ex-GM and Raidleader of the MoX Purple Kittens Raidteam on Twisting Nether (formerly Grim Batol), RIP, Winter 2010 - Spring 2013.
Armory. WoWProgress. Might start streaming Soon(tm) http://twitch.tv/szem/
Considering the price they sell D2 and WC3 on battle net website, I really doubt they would do anything for free.
Which is no excuse. Check out the microtransaction store in EQ2. It's as robust, if not more so, than games that gain 100% of their revenue off of microtransactions. That being said they still charge insane prices for things like mounts (IMO), but it was a system implemented years after the launch of the game, that wasn't planned for during development.
Blizzard DotA has already been announced, and I don't think a DotA game is technically considered an MMO.