The difference is more then just the dealer network but it is a large aspect of it for sure. After analyzing offers from all of them what I discovered is the South Koreans do not compete with Kubota or Deere on soft value. To get more specific about this the differences are: They do not offer any extended warranties, they do not offer any in house financing, they do not offer any in house insurance, they usually do not have any conveniently located dealers and they can slip clauses into their warranties that weaken them significantly.
There is really no price difference between the South Korean tractors and Kubota. It seems like there is when the dealers show you the numbers because they're not including financing costs in the final price like Kubota or Deere does. The only break you get with the Korean tractors is they offer more features for same amount you would pay for a Kubota. Koreans use this same market strategy in the automotive world.