Combine first 6 ingredients in heavy medium saucepan. Simmre over medium heat 5 minutes, stirring occasionally. Pour sauce into large bowl and cool. (Sauce can be prepared 1 day ahead. Cover and refrigerate.)
Preheat oven to 350deg.F. Season rib racks with salt and pepper. Arrange on large baking sheet. Bake 35 minutes. Cool 15 minutes. Cut racks individual ribs.
Add ribs to sauce in bowl and turn to coat. Return ribs to same baking dish. Bake 30 minutes longer, basting twice with remaining sauce.