Train buffs department.
The Swiss (and German and Austrian) electric railways use 16 2/3 Hz supply because they were initially designed in 1910-1920, and were in fact the first major AC railways, previous ones being DC apart from some experiments. They only continue with this system because of what they already have in place.
The low frequency was chosen primarily because they were using comparatively large and heavy mechanical elements for which 1,000 rpm was OK but 3,000 rpm was not. Nothing to do with the transmission but to do with the various revolving parts in the substation and on the locomotive.
Since that time any new electric AC railway system has invariably used 50 Hz. The arrival of semiconductors in the 1950s to take the place of the rotating machines sealed the point.
The railway in the US from New York to Washington was electrified at 25 Hz in the early 1930s but in recent times they did do a conversion to 50 Hz (and had a lot of changeover work to do, it must have been worth it).
http://en.wikipedia.org/wiki/15_kV_AC
If you are concerned about long-distance transmission (or, on a railway, long distances between substations, which are expensive) you use as high a voltage as you can, hence the 25Kv standard. One or two new schemes have actually gone for 50 Kv.