I actually never thought about this earlier. I'm on EU server and I realized that during night, let's say 00.00-09.00 there won't be a lot of people in WvW. Especially not during weekdays since everyone are sleeping. I think that American servers won't have this problem as much since there are a couple of hours between the earliest zone to the latest. In Europe time between the countries are balanced in like a 2 hour window.
That means, if you are playing on a weekday with a couple of friends and guilds (let's say 40 people) you can take control of a lot of castles and things since you won't meet so heavy reinforcement.
Am I thinking wrong or could this be a ''problem'' for those who likes to stay up late?