It's possible that horse meat is not commonly eaten by Muslims and Jews? I don't know my kosher/halal rules very well, but I think both groups only eat beef, sheep and goat, among the hoofed animals. Of course, there are always people in those communities who are not very strict about rules. And a "Muslim country" might have other ethnic/religious groups also living there that don't follow the same customs. Even in Saudi Arabia there are lots of foreigners (guest workers from Asia, Westerners, etc.). So I wouldn't rule out horse meat entirely without some research.