|John Francis Venture-Lieutenant, California—Silicon Valley aka JohnF|
It's not necessarily the VOs who are insisting on seating 6 (or more) players - far more often it's the event coordinators. In fact the only two tables I'm aware of that have been run recently with a limit of less than six characters have, in fact, both been run by a VO.
I know most of the event coordinators in the area where Roysier steps up to GM (who appreciate the fact that he does so). Unfortunately, though, it's often hard to get enough GMs for the number of players that sign up. This means an event coordinator has to choose between sending players home, and asking a table to seat an extra player. That's a hard call to make.
Just what restrictions can be placed on a game played at a public venue is a contentious area. You can't turn somebody away from a table just because you don't like the character they signed up to play, as long as it is a PFS-legal character. But limiting the table size is generally considered to be acceptable - in fact most places I know will only seat a 7th player if everybody else at the table agrees.
If an event coordinator pushes a GM into running a table over a voiced objection, there's a risk that that GM will stop volunteering for those events. I'd hope that event coordinators could be persuaded to take the long view, and make the decision that is best for PFS as a whole.
I'd support limiting the number of players, or possibly the total party level; a party of six 4th-level characters playing in a tier 4-6 module could well have a much harder time than a party of four 6th-level characters, especially if the party make-up isn't well suited to the adventure.