People have touched on this, including the parent article, but this needs stating in BIG SHOUTY CAPITALS:

PhDs are the last mediaeval guild apprenticeship standing, with all the ceremony and all the anachronism that implies.

Seriously. You're apprenticed to a master, you have to produce a meisterwerk, then they let you in. The entire thing is a historical accident. Remember that and everything else is... well, it's still crazy, but you can get the thread of it.

(yrs, PhD (Cantab) 2007 - http://www.lexical.org.uk/science/thesis/)