Although, like Tim Burke, I suspect that the Shadow Scholar* may be exaggerating just a trifle, I have no doubt that the ivy-covered (or concrete-covered) halls of academe are littered with undergraduates who have decided to add the price of hiring ghost writers to the price of tuition. In fact, one of my most precious memories involves an undergraduate explaining that s/he wasn't the one who had plagiarized the offending paper; it was the friend who actually wrote it. (After I retrieved my jaw from the floor to which it had unceremoniously dropped, I gently noted that this excuse didn't help their case any.) Yet so many of the excuses for students who plagiarize--it's the fault of the university system, or of boring instructors, or of corporate demands, or of pressure, or of a shortage of dark chocolate truffles, or whatever--neither take into account all the innovative, exciting, and with-it professors who still find plagiarized work making its way into their inbox, or the long history of exam and paper "hacks" (like the famed fraternity house exam bank).** Such explanations reduce a problem of centuries-long standing--when have people not plagiarized?--to something easily fixed. But if there's a system, people will game it, as various entertainment industries have discovered. Moreover, many of the "solutions" to the problem are not necessarily workable in an increasingly casualized academic environment: for example, I cannot imagine asking an adjunct teaching five classes at three different campuses (and, in all likelihood, with no office space) to interview every student about their arguments, just to be sure that everything's tip-top.
It sometimes feels as though academics are being sent off to chase the Holy Grail of assignments--That Which Cannot Be Plagiarized. True, instructors can develop assignments that are difficult to assemble by the much-vaunted (among plagiarizers) electronic cut-and-paste method, a technique that enables you to add a dollop of Derrida to your splash of Sartre and come out with...something that will get you an F in no time flat, usually. But money, whether or not it buys happiness, can certainly buy you even the most innovative assignment. ("Rewrite Bleak House as a vampire thriller, in which Jarndyce vs. Jarndyce is a nationwide cover-up for a conspiracy to transform the English court system into a haven for the undead.") There's a difference between minimizing opportunities to plagiarize, and expecting that you can find a Ring of Power that will make it disappear (preferably without turning you into a Nazgul). There will always be reasons to plagiarize that we cannot anticipate, cannot do anything about, or, sometimes, cannot explain. Which is another way of saying, to adapt a turn of phrase from John Ruskin, that perhaps we need to "confes[s] our imperfection" in this matter, and do the best we can.
*--Incidentally, this Victorianist's hackles raised at this bit: "I've read enough academic material to know that I'm not the only bullshit artist out there. I think about how Dickens got paid per word and how, as a result, Bleak House is ... well, let's be diplomatic and say exhaustive. Dickens is a role model for me." That's...not how Dickens worked. Really.
**--Also incidentally, Dad the Emeritus Historian of Graeco-Roman Egypt called while I was working on this post, and cheerfully reminisced about all the plagiarism that went on in the good old days--i.e., the late 1950s and 1960s.