Generally most people do not use the 4" backsplash and then put tile above that. It looks a bit cookie cutter to do so. The crack between the two materials is generally caulked with a special caulk that is color coordinated to the grout and it comes from the tile store. This caulk will generally need to be replaced over time, particularly on exterior walls, as the wall is affected by expansion and contraction with the weather and the countertop is not - cracks will begin to show up. You can just cut it out and replace it.