Apple capitalizes the word ‘Air’ on the iPad and lowercases the ‘mini’ on the smaller version.
On the iPod all qualifiers are lowercased: ‘touch’, ‘classic’, ‘nano’ and ‘shuffle’.

With the Mac the ‘Air’ is capitalized and so is the ‘Pro’ on for the Macbook but the ‘mini’ on the Mac mini is also lowercased.

This is a minefield. But really, I just wrote this because I want a new iPad and I can’t decide on which one I should get. Air or mini. mini or Air.