Alan Lomax once described Woody Guthrie as "an unwitting classicist, someone who understood the power and integrity of the traditional forms and sang the old songs in an old-fashioned way, his voice droning and nasal and high-pitched" (Klein 149).
Indeed, sometimes that droning, nasal, high-pitched traditionalism can make Guthrie's original recordings sound a little underwhelming. But the key to the music is that it is simple and accessible. Most people who have heard "This Land Is Your Land" probably heard a cover of some kind, because the song has been covered over and over and over. Like any good folk song, it is a song that people like to sing, not just listen to. It also tends to sound a little bit familiar even when you hear it for the first time.
"This Land Is Your Land" might have sounded familiar to people the first time around for an even more obvious reason: they had heard the tune before. It turns out the song's tune was lifted almost precisely from a Carter Family song called "When The World's On Fire," which was, in turn, based on a Baptist hymn. That's a part of its traditional charm, and not something that Guthrie had any problem with, either. "Borrowing" was (and still is) a staple of the folk tradition.