Here is a few numbers I threw together for my guild. I bought only bought one for my main account, and thats for solo toons not my boxing teams. Although they will get it anyway just to get it out of my mailbox.

Right now I am sitting in a queue for the store to purchase these for myself, and others. I started at 131,000 in the queue.
Earlier I was in the queue but had to leave for work, I started 88,000 in the queue. The queue seems to be going at around 50-70k people per hour. So lets go with the lowest one, 50k
Lets say each person is buying on average just 1 mount.
Each mount costs $25 (Pets cost $10)

50,000 x 25 = $1,250,000 per hour. And I call that a very very conservative number. I suspect this will keep up for a full 24 hours as it travels around the world
$1,250,000 x 24 = $30,000,000

So yes it appears that Blizzard just earned $30mil+ in a day for almost nothing.

Now lets look at that "limited" stock.
In 2 hours the stock has dropped by 4% so 50k = 2%, 25k = 1%
2.5 million mounts for sale. Thats quite a limit Assuming they all sell $62.5 million dollars for adding 1 mount to the game.

This doesnt take into account the pet.