I come away with the strong impression that "belief in consent" appears to equate to "I once saw a violent porn film with this practice in it, so women, including this one, must all like this sort of practice."
No, it doesn't mean that or anywhere near. Remember that coverage in the press is often highly inaccurate and sensationalised.
I fell penis first into her vagina as she lay drunk and borderline unconscious on my floor
That doesn't sound like any case I know of. However, if the victim is unconscious the law dictates a presumption that there was no consent and that the defendant knew there was no consent. If he wanted to argue otherwise the burden of proof that there was consent or that he reasonably believed there was consent would fall on the defendant. If you can point me towards the case to which this refers I will see if I can find out more.
I hadn't actually talked to her, let myself into the hotel room with a pass-key obtained by deception, asked my mate if I could 'have a go', and had sex with her from behind even though there were no indications that she even knew it was a different person having sex with her
As I say, this bears little relationship to the actual defence. The evidence of Ched Evans and his friend was that the victim was specifically asked if Evans could have sex with her and she looked at Evans and agreed. They said that she actively encouraged Evans and that, at her request, he gave her oral sex (his friend having declined to do so) prior to full sex. This was an unusual case in that the victim at no point alleged that she was raped. The case was based entirely on her inability to recall events despite, according to expert evidence, not consuming anywhere near enough alcohol to cause memory loss. Indeed, the only evidence that Evans and his friend actually had sex with her came from Evans and his friend.
I am not familiar with the other two cases referred to. I would expect a defence in the terms described to fail. As with the first case, if you would like to point me at the cases concerned I will see if I can find out more.