I'm worried that this "10 minute headway" is:
 1. Completely arbitrary. If there is no source for it, then it really should be dropped.
 2. Many of these metros have less than 10 minute headway during periods of the day. How is this accounted for?
I'm trying to get to the criteria we use to determine what is a metro system. The only reason we are having this argument is that the criteria for what is a metro is not well defined here 
No criteria should be proposed without a source to back it up. No more arbitrary rules made up by random editors.