there is still the 3 second ICD on WF, but it's not that you want the weapons to hit very slowly that makes slow weapons better, it's that both hands can proc the shaman weapon enchant, the damage of which is based on the melee hit, and you want that to be as big as possible. thus you want slow weapons. now if you can maintain the same damage output from individual hits, but can cut the time between those hits by 2/3's then you effectively do 150% more white damage. White damage is still a very significant part of an enh shamans DPS.
And enh can keep berserking up pretty good on dummy's as well, but they aren't running away from you. I personlly have trouble getting berserking to proc in any PVP, not just arenas.