I think the S versions get less traffic. I remember the 4 had people lined up for weeks.
numbered gets traffic from the mainstream
s gets traffic from the geeks
numbered usually is the form factor change... especially when it's new and sexy, it's usually the phone that will draw people in.
s is usually the bigger guts upgrade.. Big OpenGL upgrades in 3GS and 4s. 64-bit upgrade in 5s. touch id and secure enclave in 5s. etc.
funny because I've always upgraded on the s (with my first iPhone being 3GS). This is the first time I've been contemplating going 12 months to upgrade.. but ultimately decided I am going to want the s version and don't want the hassle of selling a 6 next year.
If you, after 2 years, somehow managed to keep a black and slate 5 in truly mint condition with no case or protector, then I must applaud you; you are a god among men.
the back would be godly. the chamfers would make him immortal.