Why is E the most common across multiple languages (except Lisp (which I assume is due to the parentheses))? I assume it's usage is higher because it's a vowel, but none of the other vowels are nearly that high.
E is the most common letter in the English language. There was even a fun book written without the e: http://en.wikipedia.org/wiki/Gadsby_(novel)
There is also A Void: it was originally written in French, which (I think) uses the letter "e" more often than English and then translated to English. In both cases it did not use the letter "e" at all.
I only know about this because it was referenced in a book on cryptanalysis. The simplest sort of cipher can be broken by paying attention to the relative frequency of letters in the original text. I remember a useful mnemonic for remembering the most common letters: the sentence "a sin to err" contains them. E, followed by t and a, are the most common out of those (t and a are very close).