I've had this problem for a while and now I'm getting work I don't want to miss my phone because I've put it on dead mode. Before I factory reset my phone, I was able to change my volume using the side buttons to go from different levels of sound, then vibrate only, then dead mode (complete silent and no vibrations). Now I only have different levels of sound and dead mode. I read about changing an option in sounds to vibrate only in silent mode, which will fix this but I can't find that either (my suspicians are that this option was taken out in ICS or moved to a secret location to foil my plans).
tl;dr no vibrate option when using my side buttons + sadface
I'd also like to thank you for reading.