iPod touch has been know to be deprived of GPS, Phone radio, Camera etc. However with the latest 4th gen release it seems that Apple has reduced the difference between an iPhone and iPod touch. The iPod touch 4th gen has got a Retina display, A4 processor (the same as in iPad and iPhone 4), Dual camera and even a vibrator!
The vibration alert went unnoticed for long, but it seems that Apple has felt the need to have it on for FaceTime (video calling). The iPod touch now alerts you with a vibration alert if someone wants to do a FaceTime video chat with you. Teardown pictures also confirm the presence of a vibration sensor in the iPod touch 4G.
Via
The iPhone Help
The iPhone Help