My first iOS device, back when the OS was called iPhone OS, was an iPod touch. I found it to be a great mini-computer, but I wanted it a little bigger. When the iPad came out a few years later, I bought it on day one and have found it to be exactly what I wanted, namely, a bigger iPod touch. And that's what I still like about iPads, that it's a larger iPod touch. To me, being bigger is enough of a difference all on its own to justify having an iPad -- it doesn't need separate software features to justify it. So if you don't feel you want/need a bigger iPhone, then maybe the iPad isn't for you.
I see where you're going with this, but the only time I ever thought of the iPad as a "bigger iPhone" was when the iPad 1 was introduced. The software at the time was so limited to the larger screen and the RAM so puny, I could completely agree that had things not improved in the last five years, the "bigger iPhone" metaphor could still stick.
With the introduction of the iPPro lines, I definitely don't see the iPad as a "bigger iPhone" in any regard, and I was delighted (unlike others, I'm fully aware) that Apple can now start truly marketing the iPad as a computer. Now, I don't code, edit huge videos, run Adobe software, etc., which is fine--there are still Macs for that consumer population, but I am still convinced that is a minority group outside of the MacRumors regulars. I sold my MacBook Pro in March and never looked back. I do absolutely EVERYTHING I need on my iPP as a computing device--not a Netflix or consuming device--and I absolutely DO NOT MISS the slow creep of bulk and extra tech support that was building in my OSX life that required extra "tinkering," if you will, to keep my Mac running smoothly. (I still dread adding drivers, serial numbers, and debugging my wife's Mac Mini.)
I'm not saying the iPad is without its limitations (such as the aforementioned high-end software), and I would love dual display and the ability to use multiple Airplay speakers. But these limitations aside, I really believe the iPad really could be the future for the Apple lines.
Who knows... we may look back at the new iPPs like we look at the iPad 1 and wonder, "how did we ever DO anything on this thing?"