@mano: Again, the idea is "unexpectedly" ... FDR told us that December 7th, 1941 would live in infamy. It was immediate and obvious. Freedom Summer was significant because it was White people killed -- that was significant because it woke up a lot of closet racists. Scopes I disagree with its inclusion because it was obvious to everyone involved that it was significant (it was pretty much the trial of the century at the time). Homestead strike was significant because it changed utterly the relationship between Labor and Mgmt in the US. Antietam was significant because it allowed Lincoln to issue the Emancipation Proclamation and pretty much ended the hope of Southern recognition by the European powers. The Pequot was included simply because it changed the relationship (at least in New England) between White Man and the Indian. Gold Rush was better suited to the special than Louisiana Purchase for two reasons: one, everyone knew the LP was pretty significant when it happened; two, its results took a long time to be fully realized. The Gold Rush happened overnight and the rapid population explosion in California was a contributing factor to the Civil War. Shay's Rebellion was significant because it revealed the flaws of the Articles of Confederation thus leading to the Constitution. I think I covered all your concerns.
@Dreadnought: Why Elvis? Ok, here's the argument they presented as best as I can remember. Elvis had incorporated African-American (among others) elements into his music and dancing on stage, so it started to bridge the divide between White Culture and Black Culture. Also, Elvis thrust his pelvis, and since no sex was happening in the 1950s until Elvis showed up, this is significant (ok, I'm exaggerating, but they do attribute the forthcoming sexual revolution to Elvis). Finally, and most importantly, he was mainstream counterculture (for the reasons listed above), as opposed to fringe counterculture (Kerouac, etc.). Ed Sullivan, being the highest-rated etc. show of the time, legitimized Elvis to mainsteam America like no other avenue could have. That's why it's included.
EDIT: @mano: The creationists won Scopes, not the evolutionists, so unless you think creationism leads to moral decay, your comment needs changing.