In a small bowl, combine the dry rub seasonings: salt, pepper, brown sugar, chili powder, smoked paprika, cumin, garlic powder. Set aside about 2 tablespoons of the seasoning to use for the corn. Cut the slab of pork ribs into 4 smaller sections; season the ribs well on all sides.
Drop the chopped onion into the bottom of a slow cooker and arrange the ribs over the onions. Combine the red wine, Worcestershire and broth in a large measuring cup, then pour over the ribs. Cover the slow cooker and cook on 'High' heat for 4 to 5 hours, until the rib meat pulls away easily from the bone.
Approximately 30 minutes before the pork ribs are ready, prepare the corn. Bring a large pot of water to a rolling boil and season with salt. Add the corn cobs and boil for 10 minutes. Remove the corn onto a large platter and coat generously in butter. Season with the remaining dry rub mixture; set aside.
Preheat grill to 475F (medium-heat). Remove the ribs from the slow cooker and grill for 3 to 5 minutes per side with the grill closed, allowing the ribs to get some smoky flavor. At this time, also place the corn cobs on the grill and rotate along with the ribs. Using a rubber pastry brush, coat the ribs generously in barbecue sauce and grill for 1 more minute per side.
Serve the ribs with an extra side of sauce and corn cobs with sprinkled with cilantro and a lime wedge.