Cockn-eyed

I've a grammar/linguistic question that's been annoying me for a while. What is with the tendency to use the article "an" before the word "history" or its derivates? e.g. "This could be an historical election for Democrats." My vague understanding is that you use "a" for words beginning in consonants and "an" for words beginning with vowels, but lots of people seem to use "an" for "history." Are people pronouncing History with a silent H, as though with a cockney accent? "I just read An 'Istory of the Modern World"? You don't see this with other H words, like Head or Hill. In any case, every time I see "an" prefacing "History" it pulls me out of what I'm reading and forces me to mentally correct it.