You know that you still have to pay for that Gold right? So yeah they take half...That's not exactly the way it works though. Most people paid 1 dollar per month here to turn their Live Gold sub in GP ultimate. There's hardly any surprise they reached around 20 millions subscribers basically giving subs for free. Who would refuse that gift? The money MS makes from Xbox Live subs, they already had it before, it's like PS+ money.
They definitely aren't making profit on GP right now since most of the GP subs were basically free, which is totally normal in a loss leader strategy like that.
We'll see if the business model is ok in a few years, when people actually pay more.
There are tons of MS studios now, daily costs are huge. Nobody knows if it will work or not. Let's hope so. Competition is good for prices.