Lyric discussion by knownoloudcrash 

Cover art for Empty Sky lyrics by Bruce Springsteen

just to add to what theoracle2b wrote, the difference between the two types of "empty skies" is acknowledged by springsteen in the way he refers to one as "an empty sky" and the other as "the empty sky"; while the latter references a fact that we all share as a result of the wtc attacks -- namely that the view of the lower-manhattan skyline will never again be the same -- the former speaks from the points of view of the people who actually lost loved ones that day in new york.

(i also think this subtle change in the lyrics might have been springsteen taking a shot at members of the bush administration who used 9/11 to push their political agenda; in many ways 9/11 and its aftermath became so commercialized that most of us fail to remember that there were people who actually suffered direct losses because of the attacks.)

i am by no means a big springsteen fan but this is a damn perfect song.