In your July 23 letter, you contend that "This Land" offers no "satirical comment" on the Guthrie original. You are mistaken.Link
While your view of Guthrie's "This Land is Your Land" as being predominantly about "the beauty of the American landscape" and "the disenfranchisement of the underclass" is interesting, most Americans think of the song as an iconic expression of the ideal of national unity. Jib Jab's parody addresses, among other things, the lack of national unity that characterizes our current political climate (ending with the optimistic hope that unity might be rediscovered). In short, "This Land" explores exactly the same themes as the Guthrie original, using the parodic device of contrast and juxtaposition to comment on the original. See Abilene Music v. Sony Music Entertainment, 320 F .Supp.2d 84, 90-91 (S.D.N.Y. 2003) (emphasizing the role of contrast and juxtaposition as parodic devices). The parodic comment takes on an additional dimension of irony when viewed in light of the often omitted closing stanzas of Guthrie's original.
Update: Turns out that Woody got the melody from the Carter Family
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.