Sliding VS Rolling linear slides for machinery

[gkan]

Greetings everyone,

I have a general question regarding machinery design. I have noticed that conventional machines only have dovetail slides while CNC machines usually have linear ball bearings for their axes. Even really expensive and precise conventional machines like Hardinge have sliding ways while precision CNC machinery (the ones I have seen anyway) have linear ball bearings. So I was curious, why is that? In general, isn't it true that sliding ways are generally a lot more rigid and durable than ball bearings?

Thanks in advance,

George