I sent these guys an email about this, and I got an automatic response from mathworld.wolfram.com. What's interesting is that the mathworld website does not make this error. It states specifically that this is NOT an unbiased estimator. The error only appears in the CRC version which is available on CD, though this was originally based on the mathworld material, so mathworld may have had the error at one time.
The mathworld website is very valuable, and its creator is certainly not an "idiot", though even his site does have quite a few typos. The CRC is an example of a big company exploiting the work of a kid who put a lot of time and effort into compiling lots of valuable information, as you can read about at
www.mathworld.wolfram.com. The mathworld website should be used instead, as this is being constantly updated.