And you think for some reason they aren't going to underplay/distort/hide this incident as well?
Seriously.. what the heck are we doing playing South Korea's "big brother" anyway? Don't we have our own borders to protect?
As I said earlier, I suspect that North Korea may well not believe that we sent B2s or even have B2s - although they do have a thorough spy network, they may not believe them.
As for why we are playing South Korea's "big brother", I can think of several reasons. First, every nation needs allies, and if a nation is very strong as we are, nations of similar strength are strategic competitors, so we have to ally with weaker nations. If we aren't going to help them defend themselves, why would they do that? South Korea has similarly helped us in the past. Compare that to our relationship with France, where we are legally required to defend them but they are not legally required to defend us, and it looks like a bargain.
Second, a pro-Western democracy is always worth defending, even if we are not allied.
Third, a stable world (i.e. a world whose boundaries are not continuously redrawn by war) is a desirable thing, but it isn't free. It has to be purchased with blood and treasure.
Besides, the Democrats aren't going to let us protect our own borders anyway. That would be racist. Probably sexist, ageist and homosexual too.