Well, I was (partly) wrong : While some books had DRMs, some others hadn't, following the wishes of their (self-)publishers. However, I, as a customer, had NO way of determining if a given book was with or without DRMs, except after having bought it.
After some time, I sent a mail to the Customers's Service (don't have the original mail though).
I received shortly thereafter the following mail:
In answer to your mail, here are some informations about DRMs and ouravailable ebook selection. The publishers choose whether they would like a DRM to be applied on their ebooks.
There are no limits to the number of times a title can be downloaded on a Kindle or Kindle Application. However, there can exist a limit regarding the number of Kindles or Kindle applications on wich a title can be available at the same time (usually 6).
If that limit is less than 6 (bold mine) Kindle or Kindle applications, you'll see the message "Maximum simultaneous devices : up to X depending on the publisher's limits" on the detailed description page on Amazon.fr 's Kindle Store.
Clearly, while Amazon still lets the publisher choose it's own DRMs, it adopted in France a different strategy than in the rest of the world : The "devices" mentions now books where restrictions are stricter than a standard DRMized 6, instead of mentioning whether it has DRMs at all. It is in France impossible for a customer to check the presence of DRMs given the informations on the detailed description page.
I mailed them again today, with these same explanations, and they only answered (in addition to links to the Terms of Service/EULAs) that they had forwarded my comment to the appropriate department.
Lastly, they included an email address (email@example.com) where I could send further remarks.
If some of you ARE concerned with this stance in the French Store (which may be replicated in other upcoming Kindle Stores), I guess now would be a good time to express it, perhaps by e-mailing them your own remarks on that subject.
If some of you are self-publishers, and have chosen to NOT use DRMs, perhaps explaining that your wish is not only to have no DRMs on the books but for the customers to know it wold have additional "punch" than our "customer's" one.