The French government probably offered Dassault enough subsidies that they could lower the price enough to make the Koreans think about cancelling the order unless Boeing lowered the price as well.
Standard French tactic, Dassault is (partially) state-owned.
Boeing might not be state owned, but they have 100% support of the goverment in this case. I guess that there are some "if you don't bye the F-15, we (us goverment) won't do so and so....." factors to the deal...
It's way simpler than that guys....the laws of supply and demand.
Boeing is using every trick up its' sleeve to sell product right now. The 90's were a heady profitable time for Boeing.....so profitable that companies like Boeing got used to posting handsome profits and spread sheets. Their stockholders demanded it.
Now there are a myriad of reasons why Boeing's sales have gone south (the biggest being everyone else's has too!), but all that is so much fodder for the stockholders. They want results.