Especially for the article in question, that link is not for self promotion at all. I really think that content is useful and suggestive for the article. Still for that article, I also dropped other links, which you kept, but you deleted just that one you found in other articles. I think is not fair to judge a link in relation to how it is spread on wikipedia, nor to the user who posted it, but just in relation to the article it belongs to. 
 Anyway, thank for the info. These days I'll complete the article with a new section "Probability calculus in gambling".