I remember reading the "dialect" explanation, but that just seems like "ret-con". :)
Google reports 20,900 hits for "Lloth" and 35,400 hits for "Lolth", but <a href="http://www.googlefight.com/index.php?lang=en_GB&word1=lolth&word2=lloth">GoogleFight.com</a> reports 54,700 hits for "Lolth" and...