The reason it does only 10 episodes per season is HBO has a budget of $6 million per episode including multiple units in seperate locations in seperate countries. Interestingly enough, Ireland pays about $3 million a year to HBO that specifically goes to the GOT budget... this is offset by over $20 million of spending the show brings to the area when it films there.
We don't really know if GOT is profitable, as HBO is a subscription based company and does not release ad revenue for the show. We do know that gets about 7 million viewers so it's safe to say that the show makes a ton of money. Someone earlier said it was the most downloaded show, which is true and that does cut into profits however it also creates new fans, which sells more subscriptions to HBO, and sells more books.
I will be watching my HBO on demand in a few weeks to re-watch season 4