The truth before the comics there was a part of me who thought that they might have done it, but you are right re-reading comics it´s clear that it´s the first time they do it.
It´s just that S6 it's supposed to be the darkest season and writters could have taken to another level and having Spike biting her, but instead they decided go on other direction. In many sites i´ve seen that when someone asks what other thing could have happened in SR instead the AR, some fans agree that maybe Spike losing control and biting her could have worked, and i found "curious" that writters decided not to go there and use only the sex.
If I where to hazard a guess, I'd say it's because this season is about human 'evil'. If Spike had bitten Buffy, his act would have been about his Vampirism. The AR complicates this because we can't say that what he did came out of a completely demonic urge.
In the early seasons of Buffy we (the audience) are encouraged to forgive Angel for what he did as Angelus. Part of what makes this possible is that his evil acts where so extreme (murder and world-endage).
Spike seems to have a far harder time forgiving himself for what he did to Buffy than what her did to Nikki Wood. This might be because he's able to distance himself from the atrocities he committed in his capacity as a vampire. His attack on Buffy, however, was far more personal and (considering how pervasive rape is) far less easy to attribute to his soulless vampire state. While
I believe that he wouldn't have done that to Buffy if he where in possession of a conscience, Spike can't know that for sure.
This all makes it far harder for us as the audience to forgive him, but decisions like this, to go for the harder, more complicated story is what I like so much about late the late seasons of Buffy. They could have made it simple for us, but that wouldn't have been half as interesting.
now I've gone on this whole thing without having responded to any of the actual questions on this thread, so here goes:
Day 9: How would Buffy and Spike celebrate Christmas?
I imagine that they would probably follow the traditions that Buffy and Dawn grew up with. A tree, a fire (even if it's blazing hot) and quiet evening with family and friends
Day 8: Is the scene, where Spike is handcuffed a flashback to something that has really happened or a dream about something, Buffy desired, but what never happened ?
I always read that scene as a half memory (you know how things from your life replay themselves in dreams?). We know there was some hand-cuffing going on so it's not too far a stretch to say it did happen.
Day 7: Create your own S7 (even if you think it was a great season) how does the ensouled Spike/newfound acceptance being alive Buffy interact without the FE storyline?
Every time I try to think of stuff I would change I just end up thinking of things I like about that season. One thing I would have done is change the romance between Willow and that potential who's name I can't remember. I would have liked to see Willow slowly unfurl from her cocoon of guilt and grief with the help of someone new, but that girl was so pushy and I didn't really understand what they liked about each other.
Day 6: Do you think Spike restrict from himself to bite her? With the Buffybot he seems to want to do it, is something that Buffy would allow him or not?
It's funny, I never really got the sense that he was particularly desperate to drink Buffy's blood. With the Buffybot he talked about biting her but the bite he actually gave her was very gentle. Maybe he was trying to prove that he could be in a human relationship with her. Either way, I don' think he ever bit her in a Vampire way.
Day 5: Why does Buffy ask Spike if he loves her in As You Were, if she doesn't believe he can love? What are your thoughts on this scene?
Because she's feeling unlovable and wants the reassurance. At that moment it doesn't matter to her whether his love is 'real' or not, she just needs to know that someone thinks she's worth wanting.