Ok here is my 10cents on this, like some people said, if he does not do it and someone else does, there will be issues in the bedroom, also for her to be asking, she might have been licked before maybe even with toppings so she wants to continue in her marriage.
If she does it to him, it is only fair for her to get the royal treatment too, if it is good for the goose, it is good for the gander. Besides may be that is the only way she gets hers, if that is the case, he needs to get on it quickly, it is not just about him getting his, he needs to make sure she gets hers first cos he will always get his no matter what. Shikena!