If we were only seeing Chaos Dwarves dominate in Tourneys, that would be one thing. But they do quite well in leagues, and have put together quite a record on fumbbl.
EDIT
(Before I get jumped on, I'd like to note that yes, Wood Elves have a better record on fumbbl and no, I don't think they need to get changed. They're notorious cherry-pickers and that's a different problem entirely.)
EDIT II
Purely out of curiosity, I decided to see what kind of games the top Wood Elf teams were accepting. It's possible to pull up the top 5 WE teams in fumbbl pretty easily, and you can look at their match records. The results might not surprsise you.
Team 1 - 15 Elf teams in past 20 games.
Team 2 - 15 Elf teams in past 20 games.
Team 3 - 6 Elf teams in past 20 games.
Team 4 - 13 Elf and 4 Skaven teams in past 20 games.
Team 5 - 16 Elf teams in last 20 games, including 14 Elf games in a row and counting.

[url=http://www.bloodbowl.net/naf.php?page=tournamentinfo&uname=skummy]Skummy's Tourney History[/url]