I've been here 8 years, and I've never seen their use discouraged. They're just not used very often. Over the years, the trend has been towards higher lead screws.Correct me if I'm wrong, but fast pitch lead/ball screws have always been discouraged for use with stepper motors. I believe it's because of the 1.6 deg movement of the stepper motors forces you to have a rather large movement per step.
Back then, 1/2-10 acme was common, but has progressed to today when 1/2-10 5 start is the standard (.5", or 12.7mm lead) with some people using 1/2-8-8 start, with a 1" pitch.
The majority of rack and pinion users get about 1" of travel per motor revolution, equivalent to a 1" pitch screw. But rack and pinion is more efficient, transferring more power.
Anytime you use steppers, there's a tradeoff. The faster you want to go, the less resolution you'll have. This is due to the fact that stepper motors usually have a maximum usable rpm of 1000 or less. You can't just spin the motor faster to move faster, you have to move farther with each motor revolution, which reduces resolution.
Servos, on the other hand, have a few advantages when used at higher speeds. As was mentioned, they have higher count encoders, which can give you 5 times or even more steps per revolution than you get with steppers. And since servos tend to have much higher rpm's than steppers, they are typically geared down, which provides more torque, and even more resolution. The downside to this, is that you may need to provide much higher step rates to a servo, sometimes requiring additional hardware to provide these faster step rates.
Generally, when using servos and ballscrews, you don't drive them direct. You want to gear the motor, so that at your max feedrate, the motor is spinning at 80% of it's rated no load rpm.