The "most veteran" player that i know of who have left the game have done so because of the radical changes the game underwent between 1.23 and 2.0. NONE of the players that i have ever met have left because of maintenance times. To think that long time players would leave due to maintenance down time is ludicrous.
As for the alpha and beta 1.0 players that i know, we put up with the game in its current state because it is 1: the best MMO currently available (though not the best that has existed) and 2: we have hope that it will continue to be fun and will develop into a better game.
My question to you is this; How do you define veteran players if you did not know them before the 2.0 alpha?