The mentor system has not been discontinued. However, it's not as easy as Bitcoinsummoner makes it sound to get and retain students. There are people who are on there 24 hours a day looking for students so you only really have a chance if you can compete with that. Beyond that, as you say, most students that show up aren't going to be big gamblers, they're just there to try to get free bitcoins and see what the place is about. Clearly if you get a big gambler as your student, that's paydirt but it hasn't happened to me in 4 years playing there.
FWIW, I'm level 8 and I'd be willing to sell my account for the right price.