I think it has something more to do with demand and the like. I myself was certainly not too thrilled with the Pokemon initially native to Sinnoh for example, and Platinum's additions were quite welcomed in my opinion. (Especially in the fire type department...) In some ways, I kind of feel the same in regards to BW. The available wild Pokemon, and I mean Pokemon available early on prior to the national dex, is a little limited. Since I don't want my team in Black (which I got today) to be too similar to my team in White, I'm trading over some eggs to it as soon as I get the chance. I'd rather build a team using my favorites or a team revolving around Pokemon that I would like to try out, than to build a team using native Pokemon that I'm otherwise not too fond of. Don't get me wrong though, I think Gen 4 and Gen 5 do have some good Pokemon.