If there's no 5.5", then Apple left that revenue & profit for Android competitors for up to another year. Why? For apparently no good reason as tradition, one-sizes-fits-all mentalities, and so on don't trump profit maximization. Those who are expecting to buy a 5.5" may not choose to step down to a 4.7", so there is risk that those people will buy from competitors. Again, why? No good reason. Apple is certainly capable of making multiple-screen-size models of products, as evidenced by pretty much every other line they sell.
Per sentiment on all of these threads, it appears that many/most of this crowd would not see 5.5" as an "upgrade" in a 6s, so the "holding it back" conspiracy doesn't seem to apply well to a screen size. If anything, that idea would be better supported by launching a 5.5" and then holding the more desirable 4.7" version back for the "s" version.
Best arguments for no 5.5" is the seemingly lack of much in the way of parts leaks, etc relative to the 4.7" rumors. Maybe there's something solid to that or maybe Apple "doubled down" on one knowing it would be impossible to keep both models under tight wraps? Or maybe one is going to come a little later than the other? We'll see soon enough.
Frankly, why do we care? If the 4.7" is the one "we" want and that's the one that seems most likely on the way, why do we care so passionately about wishing away a 5.5"? If the latter is not the one for us, it existing doesn't affect us in any way whatsoever. Yet, in every one of these threads, it's like the idea that there could be a different size than the chosen size is practically criminal.
I have a 27" iMac. It doesn't affect me at all that there are also iMacs with smaller screens for sale. I have a iPad Mini. It doesn't affect me at all that there are larger-screen iPads for sale. I have a 15" Macbook Pro. It doesn't affect me at all that there are other (screen) size Macbook Pros for sale, nor that there are also these whole other laptops call Airs for sale. Yet, when it comes to iPhone, that's different.
There can be only one model (and 5s + 5c don't count as two models either). Why does it matter to those who are likely to get the one they want?
It reminds me of the rumors ahead of the iPad Mini rollout. "Absolutely not!" "Steve Jobs said…" Blah, blah, blah. Then, Apple officially rolled out a second size and all that was forgotten, transformed into 1000 threads of "which one should I get?"… which, I suspect, is exactly where this iPhone train is going to end up.