The other thing I will point out is that when pros challenge they are challenging the perception of someone whose only job is to call one line from the perfect position to call that line. Often they do this after having hit a ball on the dead run from across the court. In this case I think pros challenging correctly 30% of the time is impressive and indicates how hard it is to accurately call lines sometimes ...
I truly believe that if the hawkeye system existed for rec tennis the overturn percentage would be considerably higher.
Heck, I suspect I would challenge myself quite a bit ... you know, a ball hits close to the line and I play it as good. Then after I shank the ball into the net I call for hawkeye to give me a second chance at the point.
In fact, there is probably no way I would be able to conserve my challenges to make it through an entire set. Even if I was right 60-70% of the time I could not help myself.
"You should be playing linebacker, not singles."