700k players when you:
- Don't run your own game update distribution/patcher
- Don't provide real-time chat
- Don't run your own arbitration (what's the point if mostly everything is P2P/high trust sessions and cooperative?)
- ...
700k players is great for them and by all accounts they seem to have done a great job overall, but it's a far cry from League of Legends or even DotA2 in terms of system stress.