The things I think happens:
The G75 might need some extra power from time to time, the 180W power brick seems on the limit. When this happens the good thing is that Asus did allow the battery to provide that extra power so there are no real problems.
In a session of gaming, encoding, browsing and so on the battery drop will be ~2%, nothing really major.
The interesting part is that the laptop will not charge the battery unless it drops below 95%. This looks to me like a smart charging system.
Have anyone else notice this?