While the regulation isn't great it is regulated, in a relative sense. In my own case the regulation plays out in terms of very low ripple - if the average voltage dips somewhat it's not a problem.
Sure, there are less crude ways. This happens to be one way that is sufficient for some needs. I tried it and was suprized that it worked as well as it did. I could make the argument that it should not be more complicated than necessary to accomplish the task.
I do have concerns that someone who is not aware of the shortcomings might run off thinking that this is the ideal high current approach so I explain it as best I can. Thankfully posts like this result in numerous suggestions so that the OP might realize that there are many ways to accomplish a task - some being better than others. Better could be simpler - better could also be improved regulation/ripple rejection, or efficiency, or cost. For me, at the time, this was best because I had the parts and could accomplish the modifications with limited physical effort.
For what it's worth the authors also show a PNP pass transistor with a single power resistor that maintains the regulation of the 317.
A note of caution to the less experienced people - take a close look at the inside of a quality lab power supply and you'll see that it's not quite as simple as some of the simple power supply diagrams you've seen. Look thru the datasheet on an LM317 and you'll see the simple diagrams - followed by others that still do the same thing, in a basic sense. The extra stuff is there for many reasons - some nicely explained in the datasheets - which might help to explain why good equipment isn't quite as simple as it seems it might be.
TGIF, my second day back to work. Got to get some work done.