The other thing to think about is the average person in the street doesn't think of viral pics as "viral pics". They probably think of them as stupid/funny photos, or something like that. Viral's a very "internet marketing" sort of term. That's why most of the big sites that specialise in that sort of thing have silly names intended to be catchy (collegehumor.com, evilmilk.com, funnyordie.com etc.)
Yes, you'll find a lot of references to "viral" if you Google it. But when you dig further, you'll see that more often than not the content's been written by somebody "inside" the internet industry. Kids in the playground or people in the office don't go around saying "hey, look at this viral thing!"
Google search data backs this up: "viral pics" gets just 50 searches a month. Even if you ranked #1 for the term, you'd probably get less than 20 visitors a month out of it. "funny pictures" on the other hand gets 110,000 searches.