Puddy, your fundamental impression is dead on--nothing fits perfectly regarding criteria for this distinction.
A search of the forum will probably turn up two dozen threads that discuss this difference, with each poster adding a slightly modified definition from the member who posted previous to him or her. The distinction between the two works for broad subject discussion, but doesn't hold up always when looked at carefully. So it is sometimes helpful, sometimes not helpful. Sometimes it's a war or definitions. A search for these threads over the last few years will show all the variety of ways the definitions work for the variety of members.
I'm very sorry I can't be more helpful and/or more exact.