I tried doing a search for the post here which mentioned that these were apparently a deliberate attempt by Webster to differentiate American English from British English.

I most recently read that bit of history in "The Art of Spelling," a new book by Marilyn Vos Savant (great name!!), who is an American "agony aunt" for science and language questions:

http://www.amazon.com/exec/obidos/ASIN/0393049035/o/qid=968852067/sr=2-1/103-8370088-0647806

In Chapter 10 of his "Mother Tongue," - which I happen to have at hand - Bill Bryson also makes mention of Noah Webster's deliberate attempt to differentiate American from British spelling, though he's not as categorical as Marilyn is: "All Webster's work was informed by a passionate patriotism..."