I assume because it isn't entirely complete. However, it is still a very handy resource, and I don't think enough people are aware of it, seeing as how few articles include full lists of the random booster recolours (and how a lot of people didn't think a Purple Death Driger existed).
Oh, and not to toot my own horn, but this should be very useful when working out combinations for plastics articles, seeing as there are so many combinations around where the tips just fall out or whatever:
http://worldbeyblade.org/Thread-Plastic-...bility-Doc
That said, it is always best to actually try a combination before including it, or at least get other people to try it, as otherwise a) you can't really hope to write about it in sufficient detail, and b) it might actually suck, and by including it you are recommending it as one of the most notable combinations for any given part.