My Nexus 7 was a present, my mum saved up for it bless her. And I intend to keep it for a very long time, and a plus is as it's a Nexus 7 2012 I can pop the back off without too much effort and replace the battery.
I may get a new tablet one day, but I will still keep my Nexus 7. In fact I am very happy with my tablet and my Nexus 5 phone, they are both great and perform very well. Not sure what anything else will bring thats better? More power and higher res screens is about it, if that's what you need which I don't.
But I think tablets are not changed as much because they are presents so have sentimental attachment, and because they mostly do what you want them too, no need to update, they browse the web, email, play videos and stream media, play games.