Did gays want a specific type of cake? Yes.
WOuld the baker sell the same cake to straight people? No.
Even retarded people could see the difference, dum-dum.
The question there is would the baker agree to bake a cake for a gay person's birthday.
My guess is that as long as the message on the cake didn't violate his religious aversion to homosexuality and gay marriage, he would have no problem.
As a matter of fact, for a birthday cake, the issue would likely never come up, unless the customer was looking for a lawsuit pay off.