That's not to say that I'm not excited for a retina mini, there are just significant challenges.
If the DPI/PPI of the 3/4 were sliced out for a smaller screen (making a proportionally smaller screen), the unique resolution would cause software chaos with developers. Unless iOS 7 or 8 (and all apps) can be made resolution independent.
Otherwise, the exact resolution of the 3/4 screen would have to be squeezed into a smaller package 1) creating an even higher dpi, 2) even higher screen production challenges (though apple loves those), 3) necessitating the same video card and perhaps even stronger backlighting in a smaller package, 4) with silly power requirements.
So maybe mini 3, with mini 2 sold along side at a lower price, after software or tech makes it less difficult. Meanwhile, the mini 1 is an 'awesome piece of kit' with more functionality+portability then I've ever seen.
What we use the sigs with phone brand for is diagnostic and troubleshooting. It's helpful on the many android forums to know what device someone is using without having to post "what do you have?" and wait for a response.
The likelihood of taking the time to help someone is directly related to how much information is given. You are far more likely to get help with such a signature then without if you fail to disclose what device you are running in general help.