Of late, the Newbery winners tend to be historical.
Take a look at the list since 1990. Of sixteen medal winners, eleven are historicals or historical-ish (Despereaux refers to a French princess, which has not existed to any significant degree since at least 1871); two of the contemporaries (Holes, Maniac Mcgee) are "tale-talish" rather than "straight" contemporary; one of the contemporaries (View from Saturday) is by a former Newbery winner. And The Giver, which is neither historical nor contemporary, is also by a former Newbery winner.
2005: Kira-Kira by Cynthia Kadohata (Atheneum)
2004: The Tale of Despereaux: Being the Story of a Mouse, a Princess, Some Soup, and a Spool of Thread by Kate DiCamillo (Candlewick Press)
2003: Crispin: The Cross of Lead by Avi (Hyperion Books for Children)
2002: A Single Shard by Linda Sue Park (Clarion Books/Houghton Mifflin)
2001: A Year Down Yonder by Richard Peck (Dial)
2000: Bud, Not Buddy by Christopher Paul Curtis (Delacorte)
1999: Holes by Louis Sachar (Frances Foster)
1998: Out of the Dust by Karen Hesse (Scholastic)
1997: The View from Saturday by E.L. Konigsburg (Jean Karl/Atheneum)
1996: The Midwife's Apprentice by Karen Cushman (Clarion)
1995: Walk Two Moons by Sharon Creech (HarperCollins)
1994: The Giver by Lois Lowry (Houghton)
1993: Missing May by Cynthia Rylant (Jackson/Orchard)
1992: Shiloh by Phyllis Reynolds Naylor (Atheneum)
1991: Maniac Magee by Jerry Spinelli (Little, Brown)
1990: Number the Stars by Lois Lowry (Houghton)
School librarians on the committee (especially lately as they're having to justify purchases more and more) tend to skew toward books with strong curriculum tie-in. Hence, more historicals.
Or we could be totally wrong. In any case, it's fun to talk about.