Based on my now slightly dated experiences of the system, the days of indiscriminate scrubbing are well and truly gone, although I'd hazard a guess there are still a number of instructors around who tend to be overly harsh on students, and there probably always will be despite everyone's best efforts.
That's not to say it should be all love and touchy-feeliness in the cockpit - my view is that we're after an atmosphere that's supportive and tolerant, but also expects the student to be well prepared, doing their best and willing to take constructive criticism.
Personalities are complex, and there always seems to be the odd student who has a wide gap between his or her ability and the perception of it. Understandably, no one wants to be labelled a failure, and it can be hard on all concerned at that time when Bloggsy is bouncing around the lower end of the scoring each flight and it's becoming apparent they're not really hacking it.
Some of the people who do get scrubbed can accept it and move on quite quickly, while others go into denial and take a long time to come to terms with it. No training system can be perfectly fair and equitable, and some people no doubt have been scrubbed over the years that shouldn't have (and vice versa), but it's by no means done at a whim as perhaps it may have been in days gone by.