I totally disagree. You do of course realise that there is a huge size difference between an iPad and even a larger screened iPhone, right? Where an iPhone, even one at 5.5", would still fit in a pocket, an iPad like my iPad 2 simply would not. It's not an unnatural leap of logic to think that sometimes people don't want or don't have the capacity to lug an iPad around with them. Of course, I could get an iPad mini but then that is still too large to fit in a pocket and doesn't have a phone function. A larger screen iPhone is the natural step for many people like me who find the screen on their current iPhones to be a bit too small for their uses. I currently run three phones, an HTC One for work and an iPhone 5 and Galaxy Note 3 for personal use. I would happily ditch both my personal phones and replace them with one larger screened iPhone (and possibly my HTC for another larger screened iPhone in a different colour so as not to confuse them).
A lot of people I speak to love their iPhones but the one comment that seems to come out more than any other is "I wish the screen was a bit larger."
My opinion, not a statement of fact.