Whats this about the "illusion" of friendship? They're still friends whether they want to sleep with you or not, and ultimately if they want to move things along that doesnt prevent them from being friends.
For example, a girl i like is very much my friend, regardless of whether I want to happen, is still my friend. It's not just some "illusion" i've made in hopes of getting into her pants.
Besides, yes they can. I have another girl whos a friend, and honestly she just isn't my type at all. Convenient, because I'm also not hers.