You're missing the key of threewords.me. It went viral in a small subset of users on FB/Twitter. It could just spread similarly in many other areas of FB/Twitter, you just have to seed it appropriately.
Can you give one example of this? I can't seem to think of any. There's only one threewords.me, and there's only one chatroulette. The followers most likely won't go viral.
The latter went viral on the back of press and wasn't inherently viral. threewords.me is inherently viral and has only spread in a small area of the big social graph. That's why it is cloneable right now.
There are many things that have only spread in a small area of the big social graph, but that doesn't mean that clones will go viral.
As stated above I can't think of one single instance where a clone product or derivative of a viral product or idea has itself gone viral. Whether that product is threewords.me, chatroulette, all your base are belong to us or hotmail.
May I suggest that this can go viral in several years time again? Perhaps as a remixed site of some sort? I mean its not necessary that something can't go viral again, given enough time to forget about it.
Analogy used here is to forwarded emails - every so often you find the same theme pop up again.
Is there any link or any comparison that can be made to going viral and urban legends? Urban legends end up tapping into human nature/brain wet-wiring and hence have huge longevity.
Perhaps sites which go viral have something similar?
