The American usage never made sense to me, either, but I found a reprieve during my freshman year of college: computer programming (which I refuse to spell with a single “m”). Commas are used to separate parameters in many computer languages; in this case it was FORTRAN. Quotation marks, single or double depending on the language, are used to enclose a group of characters that form a “string.” One day, our professor distributed a quiz which his secretary had typed but that he hadn’t proofread. She had instinctively corrected his “syntactical errors” by putting the commas inside the double-quotes. In a way, it was a lesson for us about the value of sight-checking our code before submitting our card decks. (Yes, it was THAT long ago!)

Using a single consonant instead of a double may have its origins in printing, saving on type, ink, and space over a longer document.

A similar situation is the practice of choosing whether to put a slash through the number “zero” (0) or the letter “oh” (O) to distinquish the two. In computer use that varies by location and by whether the data is primarily numeric or alphabetic. During orientation many years ago at the US Social Security Administration I was told they elected to put a slash through the letter instead of the number since they used numbers more than letters, thus saving time over the long run when entering data on forms and into paper records. Computers as we know them didn’t exist when the Social Security Administration started back in the 1930s.