kit lens - Is there something special about f/3.5-5.6?

The vast majority of the kit lenses sold with entry-level (or even upper entry-level) interchangeable lens cameras, tend to have an aperture range of f/3.5-5.6. This seems to be independent of whether you look at SLR or mirrorless cameras, which manufacturer you look at (Canon, Fujifilm, Nikon, Olympus, Panasonic, Samsung and Sony all make a f/3.5-5.6 kit lens) and also of sensor size (you can find a f/3.5-5.6 kit lens for all of Nikon 1, micro 4/3s and APS-C). About the only counter-examples I can find are the Pentax Q7 and Fujifilm X-E1, both of which have an f/2.8-4.5 lens. However, the Q7 with its relatively tiny sensor isn't exactly typical, and the X-E1 is definitely aimed a bit higher in the market - the cheaper X-M1 ships with a f/3.5-5.6 kit lens.

Is there anything "special" about the f/3.5-5.6 range which means that de facto every kit lens has the same aperture, or is it just a combination of engineering realities and no manufacturer being prepared to take a chance on "something different"?

Answer

It is mainly about the cost/benefit ratio of making cheap lenses. It doesn't cost a lot more to make a lens f/3.5 than f/8 at an 18mm focal length since the entrance pupil (sometimes referred to as the effective or apparent aperture) is still well within the diameter of the mounting flange used by most interchangeable lens camera systems. As the lens is zoomed out to 55mm, the needed entrance pupil for f/5.6 is just under 10mm while the needed entrance pupil for f/2.8 would be 20mm which is approaching a significant percentage of the diameter of the mounting flange of ≈38mm for the micro 4/3 format or the 44mm of the Nikon F mount. Since most lenses will be made at least the same diameter as the mounting flange, the room for an aperture of the size needed for an f/3.5-5.6 lens in the typical kit lens focal lengths is already inside the lens tube, even with all of the other things that are wedged between the diaphragm and the lens barrel.

Just to check you're talking about the same thing I think you're talking about - according to Wikipedia, the flange for Nikon F is 46.5 mm (Canon EF/EF-S is 44mm). Just a typo?

You are referring to the flange to sensor/film distance, also sometimes referred to as the registration distance. I'm referring to the throat diameter of the flange: how wide the hole in the ring at the front of the light box is, not how far in front of the focal plane it is.