I use the WASD keys but I have no idea why. I am right-handed but it feels more comfortable with my left. I have a laptop but I dont use a mouse so if a game needs a mouse its practically impossible to use the arrow keys because I can't move and click at the same time with my left hand.
WASD is really the only way to go if you have to use the mouse AND other keys to play.
Not really. I can use arrow keys with the mouse perfectly and I can use the WASD without using the mouse. I only use arrow keys when I play Exit Path or car racing games.
WASD gives a lot more room for other keys to be used in a game. (Not saying overly using buttons in a game is good.) Although, more room, usually equals easier gameplay. A lot of hardcore gamers use WASD, but you DO have to remember this is a FLASH game site and is used by casual gamers as well.
I use WASD all the time, for me it is more comfortable and it also makes it easy to use the Q,E,R,F, shift, and space keys on a lot of the games that I play.