There is a difference in terminology here I'm guessing. When we are speaking of 'one server' we mean one game world. The game does not operate on one shard of hardware. Not to mention I think your grossly overstating how many players F2P brought; as it's not even anywhere close to the amount of concurrent UU's that launch had; and the TECH should be better from launch..lol
This argument would work if we were talking about employees developing content and not IT. Companies that operate around the clock with user access will always have a tech(s) on the clock. So it wouldn't be hard for them to restart the servers during their normal 'night hours'.
Okay, so I misunderstood your statement as being "one single server for the game". Sorry. Bear in mind I'm used to working with PWE games, which have several regionally placed servers to reduce lagtime.
Also, another point--F2P may not have brought a huge number, but I doubt that the number is insignificant, either. I never specified exactly how many--and if it didn't bring a decent sized amount, why the daily restarts? A reasonable answer--albeit only speculation in the absence of a response from someone familir with the actual operations--would be to "clean out" the server memory given the increased server traffic from F2P.