more 6Sigma101  

Hi Dan

Please see:

http://www.sixsigmafirst.com/Statanova.htm

The external links policy states under "what should be linked to"

"Sites that contain neutral and accurate material not already in the article ......... in some cases this is not possible because ............ or because the site has alevel of detail which is innapropriate for the Wikipedia article"

I believe this is true of 6Sigma101.com

under "Links normally to be avoided" 

"Except where noted the below do NOT (my capitals) override the list of what should be linked to:

The only point that would seem to be of concern is:

3. A website you own or maintain .... this is because of neutrality or point of view concerns

However the guidelines do not prohibit adding these links it does say they are "NORMALLY TO BE AVOIDED". It also says they do not override the list of links. In factual explanations of statistics there are no "neutrality or point of view" concerns.
If somebody puts on an apparently commercial link without discussion, and from an anonymous source I can see the case for removing it without discussion; otherwise Wikipedia would be full of spam very quickly.
However if that person comes back and argues the case for its inclusion it is not appropriate to revert it again without discussion. You should go on to the discussion and explain your actions.

Glen