I'm typing this on my iPad & it strikes me that there's not a lot of motive to upgrade your iPad once you have one. It's a consumption device, as long as I can continue easily browsing the internet, listening to podcasts and watching movies I have no reason to upgrade.

My laptop I may want to upgrade to improve computing power and phone form factors continue to improve. Both of those things sort of affect the iPad but not nearly to the same degree. I carry my phone around in my pocket, if it's a tiny bit lighter it makes a huge difference. I mostly use my iPad at home, it's great for the things I use it for and there's no upgrade I can imagine that would significantly increase its utility.