If they get their million subscribers, something will screw up for 50,000 of them. The great thing is probably a lot of them will be easy fixes - it just requires someone to be on there to give them those easy fixes. James would be back purchasing things on XBox if there would've just been someone on the other side who he could get a hold of and was empowered to actually fix the problem. (Same with Meltzer.) The real problem is they didn't get that help in a timely manner. The big debacles don't come when there are technological issues, but when there are those issues AND people can't get the help they need to fix those problems.
When we question if WWE/MLBAM have the capacity to pull of a streaming WrestleMania, we're thinking bandwidth and servers and technological whatnot. What would probably should also be thinking about - and haven't heard much about - is the level of front line support they're going to have. That's where this is going to work or fail. (The FAQ mentions customer support will show up on the opening day, and sounds like a web chat - no phone number to get a hold of a live person.) Maybe that'll get sorted out too the day of the show. It kind of has to. The easiest way for this to get a bad rep is for it not just work, but people loudly complaining about it not working because they couldn't get anyone to do anything about it.