That may be true for the original owner, but I hand my devices down to family. I have the phones for 2 years, then trade up, and hand down. I've seen some over 5 years. Would this effectively kill that?
On the tablet side, I'm still amazingly happy with my iPad 3. It runs iOS 9 great, almost as great as my 6S+. It's a bit slower, doesn't have Touch ID or Siri Proactive, but it's a great device. I'm approaching 5 years on it. I'd go to a Pro, but I may wait until it has 3D Touch. I was disappointed it didn't come out with that.
I am considering a Apple Watch, but I'm also waiting for Gen 2, since I'm expecting more sensors and more independence from the phone. Also, I still think the battery life is too short for a watch.
So to say the life is 2-5 years, I'd say it's only true for the first owner. I buy Apple products because they're typically well made. Everyone has complaints, but overall the quality just seems higher. It does seem that some people get the latest every year, of everything: phone, tablet, watch(?). I just can't support that level of consumption. I could afford it, but I won't. I do believe the new carrier and Apple plans are starting to cater to that crowd.
I want the display, battery, and hardware to last beyond 5 years. It's one of the reasons I buy Apple. With carrier delivered devices, you're lucky to get beyond 1 OS level from where it was when you bought you device. Apple may not support all the latest features across all the devices, but I think they make a good balance in terms of performance.
So, if OLED will last, the display quality will be as good after 3-5 or more years of usage, they fix the color shifting to acceptable, then why not? That may still take another 2-3 years to realize that goal.