This thread only shows one thing, some people have no clue about paid RTS simultaneous online players.
2-5k at peak time is the standard for a good game, except for Warcraft 3 and eventually the upcoming Starcraft 2. Blizzard games are in another league as far as total players go.
600 is NOT peak. It's offpeak. When I played last night, it was 1784 online and I'm sure it still wasn't the max. 6 weeks in, it's not neither bad, nor good, it's average.
Battleforge is FREE to play and it only peaks at 5-6k for now.
Here is an approximation of sales --> online players :
100k --> 2-3k
200-300k --> 5-6k
500k --> 7-8k
1M --> 12-13k
As you can see, it is NOT linear. That is because although a lot more people are buying the game, some also stops playing and you also have to take into account the whole world and not just one particular country, which means people are not all getting online at the same time. Some people also don't play online at all, or almost never.
PS: that's not scientitifcally calculated stats, it's just to give an idea.