The original rested heavily on its '70s New York atmosphere. Many of the hostages on the train are '70s caricatures, while the city is so strapped for cash that paying a ransom of just a million dollars is a stretch for them. The idea of four men stepping onto a subway train with nobody searching their jackets and gift boxes for guns is also something that wouldn't happen after 9/11.
Likewise, the 2009 remake incorporated both post-9/11 terrorism fears and the then-recent onset of the Great Recession into the villain's motivations. Ryder was a former Wall Street tycoon convicted of fraud who hijacked the subway in order to create a panic over another terrorist attack, allowing him to make a massive amount of money via put options on certain stocks.