I think it is still applicable but not on account of someone's race, disability, age or sexual orientation, as janea has already pointed out up thread. The bakery's refusal is being seen by some as a refusal on account of the supposed sexual orientation either of the cake orderer or of the people who would eat the cake.
At least, that's my understanding of the situation.
And I feel that bakers have no business making suppositions or judgments about, or of refusing to provide cakes for other people's supposed sexual orientations during their business transactions.
Privately, anyone can object to various aspects of sexual orientation, but their objections should not be observable in public life because that is plain prejudice. A bakery shop open to the public is not private. It's for the public exchange of cakes and money, not the business owner's views on sexual orientation (or race, or religion, or disability). I think the fundamental reason for this proviso is because none of those things are harmful to society; they simply exist. No-one forces anyone to like these things if they choose not to, or if they think they have religious reasons not to, but the law says keep your dislike to yourself in public and, if there are certain kinds of people you don't want to associate with on a business footing, then don't run a business that runs on making exchanges with any kind of person who happens along.