As already stated in the comments, Angry Birds is almost identical to "Crush the Castle", another game, of which Flash versions were quite successful but mobile versions weren't. (It involves destroying castles with a trebuchet -- play it here: http://armorgames.com/play/3614/crush-the-castle).
It would have made for a more interesting article to compare Angry Birds and Crush the Castle (CTC) to identify differences between the two; as it is the article lists six attributes of success for Angry Birds:
1. simple yet engaging interaction concept
2. cleverly managed response time
3. short-term memory management
4. mystery
5. how things sound
6. how things look
Every one of those qualities is present in CTC, sometimes differently (different sound, different look) but most of the time EXACTLY in the same way (the first three items).
The main originality of Angry Birds is that projectiles are not inanimate objects but living (thinking) creatures, and the pigs (the victims) are stupid/despicable.
In CTC the projectiles are bullets and the victims are soldiers: the goal is to crush the castle but not really to kill the soldiers; the player doesn't care about them (and she certainly doesn't care about the projectiles). It's mostly an engineering project.
In Angry Birds the goal is more to kill the pigs than to crush their houses, and the player identifies with the birds. I would argue this (the story) is a key element to user engagement.