I just looked, and you are right. Senior Member is doled out at the discretion of the admins. You go from Newcomer to Member in 30 posts but there is no provision for automatic Senior Member-ship.
So yes, its a favouritism thing. Show yourself to be interesting, entertaining or amusing and participate in site stuff like the gallery, irc etc, and eventually it will come. Asking for a rank will only ever harm your chances.
Like Baz said, this is a dictatorship, not a democracy. If you dont like it, you are welcome to start your own forum elsewhere.
The greatest delight is to mark one's enemy, prepare everything, avenge oneself thoroughly, and then go to sleep.