But they have canon backstory!
That the writers tiptoe around with great care.

I swear, every single Spike/Angel fan was squealing in delight at the Jack/John barfight/makeout scene and at the same time complaining: 'WHY DIDN'T WE GET THIS WITH SPIKE AND ANGEL???' At least we got the sorta-kiss in my icon... Me? Bitter? Not at all. (This is why I love Torchwood and RTD stealing all of Joss' ideas! And sometimes his actors too...)