yeah i have heard of that too, but at the same time i am not sure if it is a verse or a hadith, but it also says (more or less meaning) that Jew and Christians are more close to you and will understand you more cos they are also the followers of the book.... so i can be friends with a hindu, a jedi, a buddhist, a fire worshipper ,a parsi who has no concept of life after death, no concept of abraham, or god of abaraham , or adam and eve, but i cant be friends with people who understand me more and i can only marry them other than muslim no one else.
seems pretty illogical to me.