Buy fewer than four pairs of $15 headphones in two years and you're still ahead. At least, you're still ahead financially; value is virtually impossible to quantify when you take into account subjective qualities like sound, appearance and comfort.
The $15 earphones last 3-4 months and I'm tired of spending an hour every few months to pick an ear phone, as well of the "music down time" that entails. That's why I started paying more. Hopefully my $60 ear phones last longer. I would rather not have to rely on the warranty.