I agree with eso on the fact that the manner in which the music is "felt" by me is way different now because of things like handling the medium, reading the booklet, wearing out your record/CD listening to it so many times, getting an almost "blue balls for the ears" condition when your walkman ran out of batteries or headphones broke, showing it to your friends, and being the first kid on your block to be bumping it....
Now, your friends have already heard it, you can get it in two seconds from piratebay (if you can get Nujabes in the space of 15 minutes without going to Japan or shelling out $50, then sh*t is CRAZY), you have nothing to hold in your hand or read, and your iPod can play almost a full day straight without needing a recharge...
BUT
I'd say that DIMINISHES the chances of a classic, but doesn't kill it. Things can still have a lasting impression. But that means leaving behind the auto-tuning, the computer beeps and blips, the desire to create a diva/boy-band/dance-floor sensibilities, and all that old mess... coming original with something that captures the attention of a large audience and doesn't grow cold, that is pretty much what makes a classic, and almost everything that you've all said so far doesn't do that for me. Maybe "Blazing Arrow"...
For instance, when "Crazy" came out by Gnarls Barkeley, that song went through the roof and had about 100 different covers of it the very next day... even Paris Hilton wanted to get in on that action... that smacks of classic track to me (that album is held in high regard, too)... I confess to liking that song... a lot, actually, and I think if I play it for my kids (when I have them) in 15 years, they'll dig it too.
I can't think of anything else off the top of my head...