You mean 37 pixels?

(640-(4*114))/5 = 36.8 pixels.

I wonder why they didn't choose this instead:

38+36+36+36+38

That would be most evenly spaced, symmetrical, and compatible with non-retina displays.

App titles. You can have less margin on the edge since you don't have to considers the app title length from the other side.

Ah, that makes perfect sense.

I guess, this would be pointless:

36+38+36+38+36 (18+19+18+19+18)

since the 2nd and 3rd icon wouldn't get the benefit of the extra spacing.

So the reasonable option would be: 34+38+40+38+34 (17+19+20+19+17)

Right, on iPhone 4 it would be 39 pixels but on iPhone 3GS and lower it would be 19.5 pixels, which would require the icons to be aliased and blurry.

Uh? Just normalize 35 on the borders and keep 38 on icons.

What am I missing for this to be more complicated?