It certainly appears that the English language owes most of its silent s's to William the Conqueror and the long-lasting influence of his imposition of Norman French on Britain!
The French were directly responsible for most of them, and indirectly responsible for some (see
aisle and
island below), but I don't think you can say that the Normans were responsible to most English words with a silent
s, and perhaps are responsible for none!
If I research just the words mentioned in this thread whose dates I can look up in Webster's 11th Collegiate, the evidence that Norman French had anything to do with the silent
s's in them is not there.
Arkansas, bois d'arc, coureur de bois, and
Illinois were coined after the New World was discovered.
The
s in
aisle and
island is the result of errors committed by etymological respellers who were influenced by the French word
isle, which wasn't adopted into English until the 13th century.
Fleur-de-lis came into the language in the 14th century, and we know it to have been pronounced with an [s] at the time because two of the early spellings were
flour de lice and
flower de luce.
And of the others:
antibourgeois (must have been coined after
bourgeois, see below)
avoirdupois 1619
apropos 1668
Belgian Malinois 1968
bourgeois circa 1565
corps 1707
corpsman 1901
debris 1708
demesne 14th century
viscount 15th century
The
s became silent in 11th century France, according to the French version of the Wikipedia, so perhaps it was silent in Norman French. But it was spelled with an
s instead of the later circumflex for a long time after that, so I expect a lot of the borrowed words containing a silent
s had the
s eventually pronounced in English as a spelling pronunciation. That might be the case with
forest and
host, for example.
I believe one of them is an "s". 
