How often do you update your iPad?
I just upgraded my launch day mini 1 to a mini 2 yesterday, so just over 2 years there, although the jump from mini 1 to mini 2 was pretty substantial. The mini 4 (God-willing) may make me upgrade even faster than before, but I'll most likely keep that one for over 3 years.
For the phone, I'm still on a launch day 4S. Yes, I know. I had updated the battery and with iOS 8 it is still going strong for me. I'll be upgrading to the 6 next month, so over 4 years there.
Just realized I'm an exception to the rule. Hahaha...