Rogues have a long history of exploiting weapon speeds for their own gain. The Barman Shanker was farmed by thousands of rogues, becoming a rite of passage in the early rogue community. While its model was unique, nobody farmed it for looks. The Shanker's unusual 2.0 attack speed dramatically improved the damage of our Ambushes and Backstabs, providing us with an amazing amount of burst damage potential.
The slow-is-best phenomenon was cropping up with the other classes as well, and it started to create balance issues. Blizzard countered by introducing a new mechanic, normalization. By adjusting the attack power formula, instant attacks no longer favored slower weapons as heavily as before. Thus began the first of many changes that have led us here to the obsolescence of weapon speeds entirely.