In the English language, there are a lot of differing rules, guidelines, and etc for the language in general, not just capitalization.
Here is another link that has different "rules", for example, you always capitalize a verb, even if it's 2 letters long. Actually, I find that
particular guideline in most places I look rather than the other way you found on that site. But the problem is that there really aren't any set-in-stone rules when it comes to the capitalization of certain types of words. There are guideline publications, like the Chicago Manual of Style, the Associated Press Stylebook, and probably others that don't come to mind right now. I know it seems strange to not really have any... "rules" about it... but that's pretty much how it is.
Perhaps VGMdb could outline what to do in specific situations with certain types of words (prepositions of a certain length, verbs, etc), or go with a certain stylebook, but also understand that even the stylebooks change over time, the Chicago one is on its 15th revision or something silly. Anyway, as far as taking that one webpage you found out in cyberspace as "correct" or something, I wouldn't recommend it, especially just taking the example of verbs like "be", "is", etc, I've always known to capitalize them.