Chris Anderson, author of "The Long Tail", in his blog introduces a fascinating (atleast to me) idea of the interplay of words, their frequency of occurance as opposed to their length, their contextual meaning and juxtaposition.
To quickly summarize his thesis, Chris cites Zipf's Law which states that the frequency distribution of words as a function of their length has an exponential distribution and the rank of these words shares a power law relationship with their frequency of occurance/usage. This was based on analyzing James Joyce's opus Ulysses and was stated, at the time, to hold true for the english language. Chris then cites Wentian Li who proves that this is the case for all languages including imaginary ones that constitute words banged out on keyboards by monkeys. Chris then concludes that Zipf's Law is more of a mathematical law in total rather than one governing and explaining linguistic features of a particular, or for that matter any, language.
Just thinking about this, one can already see that certain words (like "I") are more likely than certain others with the same length (I can't think of any right now but you are free to fill in the blanks). And this, I am sure, is a feature of the english language. There might be different relationships in different languages but there is enough evidence to suggest that all languages (real and inventented) do not follow the power law blindly. Rules of linguistic construction are the anamolies and these rules, in my opinion, were first formalized by years of talking/speaking before they were codified into a written language system. I am no linguist and certainly no expert on the evolution of languages and am shooting from the hip here but Li, in my opinion, has over generalized Zipf's Law.
Edit: A fun way to learn about the Long Tail phenomenon