I wouldn't take this law too seriously, for example from my short experiments with

    cat textfile.txt | tr '\ ' '\n' | sort | uniq -c | sort -rn

it doesn't seem to work for Polish (there's no articles in Polish, "of" is expressed as changed ending of noun, and in most texts I tried "is", "to", "from", "in" etc. are the most common with very similar frequencies).

I would think dolphins and aliens may be more alien than Slavs.