It's a very silly argument, but it seems to be very popular for some reason:

"There's nothing wrong with the RMAH because this is exactly what EBay does and they haven't gotten into any legal trouble."

Unsurprisingly, I haven't seen any intelligent arguments or debates that prove there is no gambling in Diablo 3. It's all just angry fanboys frothing at the mouths, and spitting out EBay as their only example since it's the first thing that comes to mind when they hear "auction". It's quite sad.

So, I've updated the "Diablo 3 and Illegal Online Gambling" post with several examples as to why EBay is not anything like the RMAH and why it's not considered gambling.