One Mayor, Two Mayor's, Three Mayor's, Four

 From Trish again - my genius on the lookout:

... just popped in to send you a perfect apostrophe typo for your blog - from the City of Vernon's news site, no less: 

The Provincial government’s Climate Action plan initiative prompted the Mayor’s to collaborate on the most cost effective way to accomplish these objectives through cooperation.  The Mayor’s recognized that a cooperative approach also applies to affordable housing, sustainability, economic development, water and air quality and transit – some of the major issues impacting all four jurisdictions – where cooperation could result in efficient action and a potential savings to taxpayers. The Mayor’s have instructed their respective chief administrative officers to begin work on a mechanism that would result in an action-oriented, transparent and ‘ultra-light’ approach – one that makes use of existing resources rather than creating another level of bureaucracy and an additional burden for taxpayers.

[Okay, there are only three Mayor's, but the title only made sense if I put the "Four" in there - forgive me.]

If one mayor gets together with a bunch of other mayors, do they become a... pod(?)... of Mayor's? Okay, I get the error - it happens to the best of us (well, not to us self-righteous grammar freaks, and, really, I'd like to imagine not to newspaper editors... but anyway).  But how can it be that there are other plurals (objectives, issues, savings, jurisdictions, officers, resources, taxpayers... uh, to be specific) that don't have the extra, useless, annoying, and totally incorrect apostrophe, but somehow more than one mayor gets an apostrophe? And why the capital "M"? (Don't get me started.)