From my understanding it's about cost in the end. We all know that servos maintain a better torque curve and steppers will lose steps under heavier load, hence the addition of encoders. If you go the stepper route I think it would be better served by getting linear encoders for the table instead of for the motor. It's not a bad idea on the servo side either. Although they tend to get expensive compared to rotary encoders. A user I know over at Hobby-Machinist uses magnetic linear encoder feedback to his system (not the cheap igaging ones). As a result lost steps and backlash are accommodated for easily.
with that said, I have rotary encoders on my servo system. The torque curve was more of a deciding factor for me. Plus they already had encoders on two of the motors I found on Ebay, so I just stuck with that design for the other two.