The weeping cherry is subject to borer damage, but from the photo's, it appears to have been frost cracks that has developed cankers. The tree has callused over nicely and there is no signs of gummosis or sap flux. The sap will flow from wounds and the sap turns red or orange in color and stinks.
I agree with Smallaxe that certain ornamental trees get fertilized way too much with over spray of lawn fertilizers that make them grow too rapidly and split the base.
I see from the photo's that this tree is suffering from dead under growth from improper pruning and thinning of branches. I am guilty of this practice as I trim, prune, weeping mulberry trees at Dr. Clinic's. Sometimes the offices will not allow you to perform regular trimming to improve air circulation, light penetration and new growth to occur. As these trees grow taller and spread outward, the inner branches become light deprived and will defoliate those leaves. If no production is achieved from shaded leaves, to reserve energy, the tree will shed them off.
If the tree becomes weak from drought, heat, or other cultural practices, insect will attack and can spread disease.
You can prune out those dead stems below the graft. If you prune off any of the natural weeping grafts, the tree can and will revert back to the original trunk stock tree. I have seen this a hundred times.......!!!!