Its so much more difficult to get quality traffic to a new site these days than it was a few years back. One the one hand, it may be easier to get more traffic more quickly these days with social media, but often times the traffic is equivalent to junk traffic where the owner has not developed any relationship with the Facebook crowd. They may come and go but are not going to convert.
People will say, but your Google traffic could dry up any time so you shouldn't put such a premium. But the truth is, even an offline business could have their custom dry up any time. Those are 'what ifs' that could apply to any sort of business.
Seriously, anyone that manages to buy a site for 2 years revenue must think to himself, what a fool the owner was to let it go at that price, or perhaps needed the money really bad.