Do you have some evidence for that assertion? According to their website, SSPX has a grand total of 35 "priories" in France. Hardly "very large."
I'm sorry but I read a lot of blogs and I can't recall where I saw this precisely. I can tell you that the story concerned the surprise as to why Archbishop Ricard was to receive the "red hat" as opposed to the Archbishop of Paris. The story then gave the basic account that I mentioned above: that the SSPX following was large and growing and that there was a fear that the Muslims would petition the government to convert Churches to mosques.
Here is a link from Rorate Caeli:
http://rorate-caeli.blogspot.com/2006/04/traditionalist-strength-in-france.html
It links to a PDF file which is probably in French. You can see that the issue being discussed is that the exact number of SSPX Catholics may be higher than thought. Also, the SSPX website for Econe gives a total of 65 priests in seminary at this moment (some are not in Econe but they are in France). That is impressive to me!
I am not SSPX and mention this only because I found it a surprise. I can vouch for the fact that more and more young families are turning to Traditionalist Masses (especially the Tridentine Indult in the US). The Washington Post just did a nice story on the Mass at St. Mary's in D.C. which was sent to me by several of my tradtionalist friends.
F