I must be one of the fortunate few to have the administration back me up whenever I caught plagiarists.
Although I’m in Canada, I teach for a US based private university based out of Arizona in one of its Canadian campuses. I deliver classes at both the graduate and undergraduate levels.
I have failed students on papers and in courses for plagiarism. Twice I have been directly responsible for having students expelled completely. In every case the university backed me fully. Most of the plagiarism I have experienced takes place in a course I teach on ethics, a situation rich in irony I’m sure you will all agree.
What truly amazes me is that I work for an institution that lives and dies on retention. They are a profit-oriented organization and there must be huge pressure to do everything possible to retain as many student revenue streams as possible. Moreover, students literally pay course-by-course (rather than by the semester or term)so the retention issue looms large all the time.
And yet, I was always backed fully in my decisions.
My guess is that a practical decision was made to the effect that the organization gained more in terms of reputation than it lost from the students expelled or who dropped after they were caught.
Generally I agree with the sentiment that Internet technologies make it easer to catch cheaters. It’s easy enough to google the odd sentence to see if it turns up. I caught roughly 75% of the plagiarism that way. Just straight copy and paste from the first source on the google list. Let’s face it, cheaters are not the sharpest knives in the drawer, and a significant portion are dumb as posts. Frankly, I was delighted to provide them with a practical demonstration of the consequences of poor ethical choices. 
I find plagiarism is costly on many levels. First, if well known and unchecked, it promotes further instances and lowers the morale of honest students.
Second, it costs me money. This really ticks me off, because when I find plagiarism I have to document it and spend time dealing with the issue. As I am paid a set amount for each course I deliver (I teach part time and am not on salary), each case of plagiarism represents a direct financial loss to me as it takes me more time to execute the course as a whole.
As I said, this ticks me off, a lot. So when I have iron clad proof (the only kind I ever offered up)of cheating, I really lower the hammer on the student involved.
But then, I have never denied being a small and petty man.
Third, it costs society at large. Think about that cost the next time you need surgery. Pleasant thought, isn’t it, that your surgeon may have cheated his or her way through med school? Or that the avionics crew for the commercial airline on which you have booked a flight cheated their way through exams?
And with that, I close.
Hawkwood
