Religion's only real involvement in this case is in the original prescription of the rules that unmarried couples cannot sleep together (I think? I'm no Bible expect), but the B&B couple have been quoted as saying why they established the rule in their B&B:
"We accept that the Bible is the holy living word of God and we endeavour to follow it as far as are able."
Depending on your beliefs that either is or isn't a 'Christian' thing. I am not religious, and as such I do not see it as a Christian belief, as much as a reflection of the mind-sets of most people at the time. The problem I have with Christianity is that it enforces (or at least has enforced) and encourages those mind-sets in modern day. I think whether you say couples should sleep together before or after marriage is aside from this case - the rule that the B&B owners were imposing means that gay couples can never sleep together (Well, except those that are married, of which there are many all around the world. I wonder what would have happened if it were a married gay couple from California who wanted a double room?). Essentially, it's the couple’s personal choice to believe in the words of the Christian Bible that is in effect creating the discrimination.
However, I certainly agree it isn't fair to tar all Christians with the same brush, and I don't think it's all that much of a brush even if we were to. I have gay couple friends who consider themselves good Christians and I'm pretty sure they've slept together! This couple have only been found to be discriminating on a legal technicality in conflict with just one of the many teachings in the Bible that they probably follow. I also suspect that the B&B owners are really, genuinely nice people who did not intend harm, even if they have potentially caused it.
I think the reason for the headline mentioning 'gay' is that discrimination based on the decision to get married/partnered is deeply entrenched in law, especially so with regards to finances. I think similarly the headline "Unmarried couple not allowed married couple's tax allowance" is a lot less extraordinary than "Gay couple in civil partnership not allowed married couple's tax allowance". The former is (whether right or wrong) 'accepted' prejudice, whereas the latter isn't. In the case of the hotel bed it's slightly trickier, and they would have probably been able to discriminate based solely on marriage OR partnership, but evidently not just on marriage.
I definitely agree that people are too quick to play the discrimination card. I get teased (about my sexuality), and in return I tease those people about their notable deviations from the norm, or play to the stereotype a bit for fun. But that is banter. That’s fine and I think anyone who cries discrimination after a funny joke or similar is a bit of a lamer. The problem is when it isn’t banter and where things are said with deeply hateful and malicious intent. At that point it almost doesn’t matter what the subject is, it just isn’t right to abuse people like that. When it happens it’s sometimes the case that the person on the receiving end has some legal protection to get back at the aggressor with.
In this case, as I said, I am certain that the couple didn’t mean any harm, but they have caused some. If a friend was to make a gay joke at my expense and it genuinely upset me (unlikely, but could happen), I’m sure they’d apologise and withdraw the comment. Conversely, while the B&B owners have apologised for the offence, they are unwilling to change their view - by doing that they have openly stated “A straight couple are welcome to sleep together in our hotel, but a gay couple are not”. The gay couple were as close as possible to being married under English law, and the law says they should be afforded the same rights as straight married couples. It’s the discrimination based on marriage vs. civil partnership that is at the crux of this entire case. As marriages are exclusively for straight people and civil partnerships are exclusively for gay people, it drags sexuality in to the debate with it.
Anyway, I'll stop now, as I feel like I've really rambled on there as I don't really know how to conclude my post