I can guarantee particles would be a great deal slower if they were implemented using Physics. Particles are actually pretty lightweight, but they tend to strain the renderer if you spray thousands and thousands of them.
In that thread the user said they were using iOS 5, which is pretty old now! iOS 7 is waaay faster, and it looks like on page 2 they resolved the performance issue as something else (it wasn't particles).
Space Blaster runs a nice 60 FPS on an iPad 2 with iOS 7 for me. What have you been testing on?