The independence of sources, of course makes it tougher to substantiate the Real World notability of a fictional subject. However, it also means that information is far more likely to be balanced and objective. While editors look for good, solid sources, there are easy parent articles for editors to build up. We don't need 6000 articles on each pokemon, but articles on Pokemon - the game, series, movies, merchandising, controversies, can all be made. The 6000 animals are simply unimportant, because they're nothing but merchandising, and where are they covered? In the books published by the company that makes the game. But the results of that merchandising in sales and so on are important and notable and have a lot of independent coverage.