I think what you are referring to is a crab drive.
The biggest difference is that with all 4 wheels being steered together you can no longer have true holonomic motion. With a 4 wheel swerve you can turn all 4 wheels perpendicular to your point of rotation. Causing for 0 scrub when turning with your pivot point being anywhere(large banking turns).
Also using that much chain running around your robot is a nightmare to design around, It also adds up in weight after a while.
The ability to have full holonomic motion is the number one reason our team went with the swerve drive.
We use belts for all of our stagings other then the bevel and the chain in the lower pod. The reason we did not switch the chain out to a belt in the pod was that in the final staging a 9mm belt would not transmit egnuf force with out breaking or wearing.
Here is ours. Our only problem was the encoders slipping and one getting destroyed after we received a catapult shot to the encoder assemble. As always thank you 1640,2471 for cad and good design examples.
http://www.chiefdelphi.com/forums/sh...d.php?t=124664 A