The $5 fee, whether it's small or not, still requires people to pull out their wallets. A lot of people simply don't want to get out their wallet and go through the sign up process, so they won't.
A lot of their news is available everywhere else. Why would I need the NYT.com website to read about Obama winning when MSNBC.com had it for free? So the question should be "Are our op-ed's and in depth reporting worth $5/mo?" And if the in depth reporting is big (e.g. CIA eavesdropping scandal) it will be covered elsewhere shortly after it breaks.
So the number of page views they lose to $5 kills their advertising dollars. Is that $5 really going to make up how much they're losing? Not according to this post: http://www.niemanlab.org/2009/04/paying-for-online-news-sorr...