A large portion of World of Warcraft and other MMOs is the scope of the game's economy. I've been hearing rumors about the WoW Gold (piece?) being labled as a known and accepted form of currency somewhere, but I'm not sure.
Really, at the software can and does damage that economy, throwing off the balance of this economy. I'm a former player that used to try and make money through auction house deals and I slowly saw servers starting to decline economically as more and more goods flooded markets, with no real gold anywhere to spread about.
This may not neccesarily be the fault of Glider itself, but it certainly is a supportive factor. As for lost revenue, when someone's found to be botting, they get banned, and revenue is lost, it's that simple there.
My opinion is biased as I was a player in a server with a ruined economy and rampant cheating, but I kinda hope Blizzard wins this one, despite the arguments used. I'd rather the sale, distribution, and development of Glider be stopped/halted.