i think it's because of the hgh effect, most of the older teams with money are sagging because their roid users are coming off the drugs, and the younger teams (marlins, rays, d'backs, twins, angels) were less effected than say the yankees because most of the young players didn't have the money to get roids and were less likely to be roiding than the older guys with money.
i think the marlins are a fluke and will fall back to earth soon and the rays are for real and will challenge the yankees and red sox for the al east and may make the playoffs. i would love to see a marlins vs. rays world series though.