They could even surround the screen with a different set of touchsensitive sensors for these types of controls, effectively making it pseudo multitouch. You can still get precise one-point control on the screen while your other finger manipulates image zoom level, rotation and whatnot with the second set of touch sensor around the screen.

how come Angry Birds has pinch and zoom?

I can't zoom in angry birds rio , I'm doing it wrong or I need to install something ?

You don't need to install anything extra. The pinch to zoom does work, although it's a bit unreliable and takes several tries to work.