Rogues have to consider their positioning as part of the rotation. Also, sub-35% you ARE gcd capped as assassination. You have twice the energy that you need, and the rogue GCD is 1 second. On Occuthar sub-35% I am constantly on the move as the tanks never seem to get that you don't need to stand 180° to each other. Constantly on the move = my mouse is nowhere near the action bars and if I don't use my abilities I don't do any damage. Same goes for pretty much all melee. If you want a Firelands alternative, Shannox, Beth'tilac, Alysrazor, Rhyolith, Baleroc (to a lesser extent), Majordomo and Rag (OK so all of them) all require high dps while moving, and they require an accuracy of character steering not possible with WASD(QE) alone.
Also, for classes like rogues, they're for the most part not capped by GCD but by energy, is you don't let your energy get full AND do the right rotation there is quite some leeway on when you use your abilities so clickers are not at less of a disadvantage.
Using WERSDF for movement is better than QWEASD, you gain 3 base keybinds left and right of the movement keys (QAY(Z) and Z(Y)HB) which can also be mapped with +alt, +crtl, +shift for 18 additional binds without stretching your hand unnecessarily (even more if you use combinations of modifiers) and you can also reach N and M with your thumb.
On another note, who has taken the next (obviously superiour ;-)) step which goes from mouselooking to mousemoving. Unbind your WASD and do all the moving of your character with the mouse, man I love the freedom my left hand now has.