It is just a different stylization of the name, and only the name of the device... A stylization is a different way of writing something to make it look more catchy, or cool, ... you get the idea =)
From Wikipedia: "Stylized" may mean the adoption of any style in any context, and in American English is often used for the typographic style of names, as in "AT&T" is also stylized as "ATT" and "AT&T."
So, "iPhone 5S" is stylized as "iPhone 5s."
Here are some other examples:
Lady Gaga's upcoming album is legally named "Artpop", but stylized as "ARTPOP"
The band Nine Inch Nails' logo features a stylized version of their abbreviated name "NIN," to wit: