My mistake then, I should do my research as well. I always reckoned that the number of guns able to do a lot of damage to civilian areas within the Seoul area (if not central Seoul) was uh... let's just say a lot more than 120 barrels, by several orders of magnitude!
Still, I think the political implications still stand - it might not be Seoul by artillery as such, but there is pretty massive destruction that the North could cause in the first few minutes and hours of a conflict to the South's population and economy.