but years ago when I was at Cruising world one of the ad salesmen clued me in a bit.
With paid subscriptions you can get an audit, which shows the advertisers exactly how many magazines are being distributed via subscription and newsstand sales. Ad rates are based on "eyes on the page," so the subscription people have to keep a hand on the throttle. Subs are off -- offer the free tote bag or wind jacket to get a few more to sign on.
I don't think a free mag gets the same kind of audit -- how could anyone realistically count the number of mags that went home with someone rather than into the bin?
Good Old Boat has chosen to be subscription-driven rather than ad-driven, hence the higher content/ad ratio. People seem to like that and are happy to pay a little more for it.