The official word from Wargaming.net is:
We will soon be updating the World of Tanks in-game store. As of January 16, 2012, the Type 59 premium tank will be removed from the in-game store after the server restart, which will take place at 6:00-6:30AM EST (11:00-11:30 UTC). While the tank will not be available for purchase, all existing Type 59 owners will keep their tank intact.
This decision has been made to ensure a healthy gameplay balance at higher tiers, and also to encourage a wider variety of tier 8 medium tank usage. If the Type 59 becomes available for purchase again during special events in the future, we will be sure to provide ample notice.
Again, the Type 59 will be removed from the in-game store on January 16, 2012 after the server downtime scheduled for 6:00-6:30AM EST (11:00-11:30 UTC). If you are considering purchasing the tank, we encourage you to do so before this point, as it will not be available for purchase as of January 16, 2012.
So the official line is game balance at higher tiers. And certainly one of the complaints about the tank is that a lot of them show up in those battles, relative to other models.
However, a suspicious mind might see something different at work here. After all, the Type 59 has been in the game for a while now, and it was controversial from day one. Why change now? Maybe sales of the tank have finally slowed? If everybody who really wanted one already has one, what better way to prod those on the fence about the tank than announce that it is going away?
I have one in my garage.
And it quickly became my favorite tank.
As an extremely casual player… I play 3 or 4 rounds every couple of nights… it has allowed me to play in the higher tiers, where the skilled players seem to be and where the battles are thus more exciting. And the fact that it is a money making machine has allowed me to pursue SP gun ambitions. (There are no gold SP guns.)
I expect that there will be a flurry of Type 59 purchases this weekend, and that we will see it dangled as a special limited time store item in the future.