Even if JLU sold 'well enough' on Matty, it would have to had sold fast enough as well. Because, by Matty standards, it has to fly off of the interweb shelves faster than a Wind Raider delivering Domino's Pizza. So yes, by those standards, Justice League Unlimited was a 'failure'. It was and is such a failure that Matty is still releasing/will release JLU product throughout 2012 and possibly into 2013 depending on how well the upcoming packs are spread out.
'...because the minute a little girl is trampled by 100 teenage girls trying to get to Justin Beiber at the Tea Cups, you will be wondering why the hell we make poor Justin Beiber stand in a 30 minute line and create an unsafe atmosphere.'