North Korea doesn't have magical 152mm or 122mm artillery that enables it to reach Seoul.
Lol.
Yes, North Korea doesn't have magical 152mm and 122mm artillery that enables it to reach Seoul. There's no 122mm system in the world that could reach Seoul from the DMZ. Likewise with 152mm pieces (Maybe some RAP that could hit the extreme edge?), nor the 130 and 120mm pieces in its inventory which combined with the above constitute the overwhelming majority of its artillery forces. It DOES have 170mm
Koksan SPA systems which could with RAPs, but that's about it. It also has a couple hundred 240mm rocket launchers and a few dozen 300mm that could reach.
Of course once these systems open up they'll be subject to counter-battery fire and airstrikes and the long-range systems are some of North Korea's best. It would be dubious military strategy to use these to scare the residents of Mapo and Eunpyeong and blow up a Tony Moly. So while some are no doubt there for deterrence, it is probable that most are in reserve for use against actual military targets.
Anyways, how you took that above sentence to mean "North Korea can't hit Seoul" is beyond me. Unless you thought they didn't have 122 and 152mm pieces Or thought that North Korea didn't have the some magic version of those or something...I don't know.
But anyways, to most people in the know, they don't have to do the above explanation because everyone knows that super-heavy artillery units (170mm~203mm) with those kinds of ranges are far less numerous than light 105~122mm and heavy 152~155mm systems.