Some experts claimed that when an ‘o’ follows a consonant it must use an ‘e’. But there are too many exceptions for that to be a rule. Other experts claimed that the rule only applies to ‘English’ words and not imported or exotic words. But that excuse fails when we look at all the exceptions. Others claim that it is simply keeping the spelling in line with words like ‘toes, hoes, and shoes’.
Today, most dictionaries offer a choice of endings, ‘cargos’ or ‘cargoes’, and most people, quite sensibly, don’t bother to add that obviously unnecessary letter: After all, we all know that the silent ‘e’ is used to alter the sound of the vowel that preceeds it. This one does not.
To add a letter that serves no useful function is a waste of time and ink, as well as being an impediment to the student (both domestic and foreign). Today the ‘e’ is quickly vanishing from the plural of words that end in ‘o’ and we have cargos, dominos, mosquitos, mangos…etc.
Unfortunately, we still have a few purists fixated on the archaic and fighting a loosing battle who insist on ‘potatoes’ and ‘tomatoes’, but the rest of us are quite happy with our mangos, avocados, pianos and banjos, knowing that it will take a few more years but inevitably, potatoes and tomatoes will lose their toes.