Saudi Arabia is not as the article says , just an ordinary "homeland" for Muslims it's "holy land". This is why Saudi Arabia doesnt ask to build a Mosque at the Vatican City (Italy). I dont think Moscow is considered "holy land", therefore its not a fair exchange. You'll find thousands of Churches in every other Islamic country.
Furthermore, you wont find 2 million Christians in Saudi Arabia, so what use is an empty Church?
I understand your logic above; however, how come to Orthodox Jews, all of Israel is Holy Land (also), yet the place has some of the most holy sites of Christianity and Islam. Perhaps, this reflects Jewish largesse?
And, to reply to your last thought about what good is an empty church, it might be good for symbolism. You know, like a Menorah next to a Christmas tree in many office building lobbies.