My partner and I have this same issue recurringly so I am very sympathic to your wife's position, but the one thing I have learned is that this is very difficult to change on a consistent basis, but it's well worth the effort.
When two people love each other there is a natural desire to be in physical contact. When you are in a comfortable non-affectionate relationship one partner feels they are always making in the extra effort for physical contact and the affection is not returned.
Make this a daily effort, there is a fabulous book called the five love languages that gives wonderful tips on understanding the way she communicates love and being able to share that language with her.
Don't expect any miracles, she probably loves you but has long since given up on the fact that she can get what she wants in a relationship with you. Take things one day at a time and keep me posted ;)