Two domestic firms for every foreign firm retained?

The same survey that stimulated my ruminations on the meaning of “foreign law firm” (See my post of June 26, 2009: the term “foreign law firm”.) offers more data on those firms. According to Met. Corp. Counsel, Vol. 17, June 2009 at 11 (Marcus Linden), based on a survey population of 191 US legal departments, “The average number of U.S. law firms supervised was 38.6 firms per law department, and the average number of foreign firms was 18.9 per department.”

It surprises me that the US legal groups retain about one foreign firm for every domestic firm. I would have thought that domestic firms would significantly outnumber foreign. On the flip side, if a company does business globally and has only one or two firms per country, the number of foreign firms mounts rapidly.