Update of app shown in iPhone but not in iPad?
From what I've noticed with universal apps, and also with iPhone only apps between my devices is that sometimes an update might come one day to one device and the next day to another and at the third day the last one gets it. Might be that Apple does this so their servers wont be overloaded when everybody updates the same app at the same time.

You should also check that you've released the update to all platforms, not only iPhones.