Well with my experience, I believe they can be just friends. However, the idea of those 2 friends being more then friends, ALWAYS comes up. I don't know what it is, it might be the fact that the 2 people have such an amazing friendship that they believe a romantic relationship would be amazing too.
When I was in college I had a male friend that I developed a crush for but when I found out he had a gf, obviously that crush vanished. After a couple of months, him and his gf broke up and somehow, he found out about my crush on him. Then we became closer friends and he asked me out on a date which I agreed to but it was just so weird. That day was the day that I realized, we would just be friends. Afterwards, we would hang out and do fun things together but he would always joke about us dating, going out together and being intimate that it just became annoying. We're not close now, which is sad but it is what it is.
Also while I was in college, I was completely gaga over this one guy. He's probably one of my greatest loves. Anyways, his best friend who I was friends with, tried to flirt with me so many times. When I wasn't speaking to the guy I was gaga over, he started talking to me more and more and tried sending me pictures of himself. It was so funny (now that I look at it) because I never was attracted to him and all I ever was going to him was a friend. He just completely showed his true colours which made me not like him even more. I don't talk to him anymore. I do see him here and there and I am friendly with him but I think he got the message when I started being a complete bitch towards him, haha!
One of my closes male friends today, has never made a pass at me which I really respect. We confide in each other a lot and our friendship is great. I talk to him about guys and he talks to me about girls. One time he was dating a girl, who was completely crazy! She mistook our friendship for something more and created a lot of problems. It's funny because me and him are not attracted to one another at all, so I don't understand what she saw. She would complain when he would drive me home, she also complained to him that we were to close and that he would pay more attention to me then to her. They're not together anymore, they're just friends now. But I absolutely can't stand her and she knows it. She won't say a word to me because she knows that I have nothing to say to her.