Suffice to say they're different. Many States do not have a Master's Classification.
See for yourself: http://www.contractors-license.org/
Who constitutes this "most" that "say"? (I'll bet it's the holders of the Master's Classifications)
The C-10 classification has been around since at least the 1930's, and the Journeyman Electrician's Certification was recently implemented.
This doesn't mean that everything was a hackfest free for all prior to the implementation of the Journeyman's Certification.
Both require an in depth exam.
The C10's exam has a section devoted to Contract Law.
The Journeyman's Exam has no such section.