Three comments:
-If Blizzard released numbers from their free trial program, I'd imagine that 90+% of trial accounts are banned within their first 90 MINUTES for advertising RMT in game. Even at face value, if there are 20Kish odd signups on a daily basis and 10% of them stick around, that's 2K new user accounts (correlated with, but not equal to, actual new users) per day. That would mean growth as long as you aren't losing greater than 2K longtime users per day.

-I'd imagine that a non-trivial number of those "lost" accounts were actually single-purpose to begin with. E.g. my favorite author/politician/archnemesis/etc is making an appearance, and I'd like to go listen/cheer/throw disembodied genitalia. Of course, having someone show up for an event is an opportunity to get them to stick around, but most online games probably don't have to deal with "losing" people who literally showed up to do a single event.

-As many naysayers on other threads are glad to point out, SL is not really a game. No amount of customer service, tech support, orientation programs, voice chat features, documentation, etc is going to turn it into a game. People who show up expecting a game, and instead find a bizarre strip mall where everything costs real money, are going to be very hard to retain. Orientation programs are going to give misleading short term retention numbers if the user is sitting there thinking that all they have to do is finish this orientation and then they get into the real game (e.g. mining asteroids while waiting for skills to train in real time before you can start serious PVP in EVE). SL is not for everyone, and having new players get hit up for in-game currency that costs real cash as soon as they hit the open grid only helps force a decision on the player's part sooner rather than later.