It seems you can thank Noah Webster for dialog:

http://en.wikipedia.org/wiki/English_orthography



>>>(btw, if dialog should actually be dialogue, epilog an epilogue, etc... then we better start writing all the words ending with a -gue with a -g or vice versa... so, either vog, seg, leag, dialog, monolog, or vogue, segue, league, dialogue, epilogue, dogue, blogue, smogue, clogue)
>>
>>FWIW, I use "dialog" for the modal form in an application, and "dialogue" for what's in the movie script.
>
>That's like the fine distinction between disc and disk - and nobody uses disque, because they'd risk the appearance of a pinque guy who'd say "it's actually risque, don't you thinque?".
>
>Thunderbird's spellchecker (set to US English) redlines dialogue, monolog and epilog, while dialog, monologue and epilogue are OK. No logic, just a list of exceptions, aka dictionary.