First of all, the iPhone already has 4G. Secondly, The New iPhone? What kind of name is that? Just think of the 4S as the "4.5".
If Apple did what you wanted, it would go 4, 4S, 6, 6S, 8..... No odd numbers.
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LTE isn't the only 4G out there. The iPhone already has 4G, actually.
No.. LTE isn't even 4G.
4G is minimum of 100megabit. LTE Advanced supports that.
So today there are not a single REAL 4G product.
But WHY people wants 100 megabit into their phone/tablet is another thing. Especially in US where data caps are small/expensive.