Well, maybe it's to signal "I have the latest!" (as opposed to a few-year-old one) rather than "I spent $70 more!"
But I don't get it either. I always bought my iPhones when they did the hardware revision (the "s" models), not the design change.
It's like how folks said Starbucks cups were a status symbol. On what planet does $3 buy you status?
The LTE version is only $70 more. That's not going to wow anyone. (Well, plus a monthly service charge, which is more significant financially, but has no weight as a status symbol.) Meanwhile, there are more expensive upgrades that are at least as obtrusive, like the stainless-steal case and those designer bands.
I mean, I don't really get it either, but it isn't this.
Maybe it's just a way to highlight a significant new feature?