I wouldn't buy the memory course, either, but not because there isn't some value in it; there may well be a lot of value in it (I don't have it), but this sort of memory help is available through a few select books without spending big bucks. Harry Lorayne, mentioned above, is a great place to start. Some stuff by Derren Brown, too, though his stuff is buried in the midst of other things.
As to how difficult it is to memorize 52 cards, as is said above, with practice and memory techniques, one can do it in a few minutes with the right training and practice, though that is not how Karol did it on Stern or Ellen. As DA points out, he has one stack that he has memorized. You can take as long as you like to learn that stack, and it appears that Karol took a deck, shuffled it until he was satisfied that it appeared random, and memorized it. That's how I'd do it, too, but there are even easier ways that I won't go into except to say that in setting up the stack one can make it appear random while in reality the suit and value of one card gives a clue to the suit and value of the next so even if you forget the stack you can get back on track by working the simple algorithm that's built in.
As to the professor who memorized the class names and details, that takes practice but again, not so much as it at first seems. I was at a seminar with thirty people I had never met about six years ago. The seminar leader spent the first half hour instructing us to do something similar. The first person in class gave their name, hometown, job title, and one or two other things. The second person repeated what the first person said then added their own info. The third repeated the info of the first and second then added their own and so on.
By the fifth person, people were stumbling a lot and needing reminders. By the 10th, very few remembered anything of consequence. Perhaps three or four people got about 50% right, but in a stumbling fashion.
At the beginning, I saw that I would be the last person to go so I immediately began employing some techniques I had read about but never used, and I attempted to cement every person's info in my mind. When it got to me, I turned my back on the room and recited all the information without error not quite as fast as Karol in the video but at a steady rate.
Everyone was impressed, and I was pleased with the little validation of the things I'd read.
You have to actively engage to do it, though; you can't half pay attention and expect it to work.