Sort of agree...
I'm in a lucky position to have had a few tablets, both iOS and Android based they all do what they are designed for (media consumption) very well, personally I prefer the Android system but iOS is good if somewhat overrated. the problem i have with tablets its their main attribute, size.
Too large to fit a pocket means I will normally use my phone unless the tablet is in arms reach, this is why so many have become coffee table devices, this is where I believe most will exist well into the future, and that's a good thing as its where most people feel comfortably (in their lounge watching tv) browsing the internet , playing the odd game , reading / writing emails etc.
this is where the price become so important, Apple pitch high, their customer base is happy to pay high but really a secondary or tertiary device (after computer or laptop & phone) should really be in the sub £200 bracket. I suspect this is what Amazon will go for at least with its budget device.
basically phone is with me everywhere, computer / laptop is for everything and tablet is for lazying on couch reading news and generally slobbery computing.
I have noticed that many of my clients who own iPhones or other smartphones with 3-3.5" screens seem to use them more than people who own newer phones with larger screens i.e. SGS2 etc
I think when limited to 3.5 inch or less on your phone the tablet is more necessary, when you have super amoled plus 4.5" gorgeousness :D tablets get less use.