Woody Guthrie's copyright used to defile his memory in lawsuit threat

Two brothers who cooked up a funny parody of Bush and Kerry singing "This Land is Your Land" have been threatened with a copyright infringement lawsuit by the current rightsholder to the classic Woody Guthrie song, a company called Ludlow Music. A lot of the copyright rhetoric centers on copyright's ability to give creators controls over their works, but here it is working just the opposite, for Woody Guthrie's standard copyright notice went like so:

"This song is Copyrighted in U.S., under Seal of Copyright # 154085, for a period of 28 years, and anybody caught singin it without our permission, will be mighty good friends of ourn, cause we don't give a dern. Publish it. Write it. Sing it. Swing to it. Yodel it. We wrote it, that's all we wanted to do."