It's easy to think that there's some deep reason behind things like this; quite often, it's based on something like simpler:

Alone in a room in his home in Bonn, Germany, Friedhelm Hillebrand sat at his typewriter, tapping out random sentences and questions on a sheet of paper. As he went along, Hillebrand counted the number of letters, numbers, punctuation marks and spaces on the page. Each blurb ran on for a line or two and nearly always clocked in under 160 characters.

That was back in 1985. It's kind of interesting to note that texts sent now are based on the size he came up with using a typewriter to experiment with...