"These used to be concepts you could write 100 pages on. Now, any one of these issues would be solvable in a matter of minutes. A good love story may still transcend time, but these days, if your characters don’t even have cell phones, how genuine to real life could they be? These days, Harry probably would have met Sally on Match.com and that orgasm scene in the deli would have been Billy Crystal watching a video of Meg on his iPhone. Steve Martin wouldn’t have had to sit in the bushes and whisper words to another man to woo Roxanne – he could have just texted her from the other guy’s phone. And John Cusack wouldn’t be standing outside Ione Skye’s house with a boom-box over his head– he would have just thrown his iPod into her open window and screamed “Track 4!”
There's also the whole "relationships are temporary" thing too.