Some coastal regions of the world have cooler summers and warmer winters than inland regions at the same latitude. What accounts for this difference in climates?

It depends on where you are in the world in relation to the latitudes and also it depends on the type of ocean current that is off the coast. However, regardless of latitude and currents, the ocean acts as a large heat sink moderating the temperatures of coastal areas from the extremes that can be found in inland areas. The ocean changes temperatures much more slowly than the do landmasses, and as such, influences the overall temperatures, slowing the rate of change. This property of water is evident when contrasting the amount of energy required to heat water vs. air. In the kitchen, the energy expended to heat the amount of air in the oven to 200 degrees is significantly less than the energy required to boil a similar mass of water.