A major advantage of SMD is the ease of machine assembly .The automation of the assembly process gives more uniform results.When it comes to testing PCBs mistakes tend to also be uniform which makes things easier .         If all assembly were to be done by machines then it does not matter much from a cost standpoint where the machine is located.This gives the customer the choice of where they want to do thier manufacturing .When you have through hole stuff with lots of flying leads and heatsinks there is a large part of the job that has to still be done by hand .The cost of hand assembly varies greatly from country to country .