Does it really?
Below is a link to an article that seems to dispute that claim. Here's an excerpt:
"A thoughtful reader kindly sent me a fascinating article on cutting boards. Originally published in the Feb. 6, 1993 edition of Science News, the article describes research claiming that wooden cutting boards possess some sort of bacteria-killing properties, thus making them less likely to contaminate food than plastic or acrylic cutting boards. "Pathogens prefer plastic," the article declares.
Nearly twenty years later, however, experts are still recommending nonporous plastic cutting boards, and local health departments continue to prohibit the use of wooden cutting boards in commercial foodservice."
Wood Vs. Plastic Cutting Boards: Which is Better?
And another, similar, article:
Cutting Boards and Food Safety
For every article that claims one thing there are other articles that claim the opposite. I honestly think that the most important thing is that as you clean your cutting board after use. Short of that, it doesn't matter all that much whether it's wood or plastic.