Agree with your point, and in fact I was fortunate enough to be able to fly the spouse and kids over to Europe when we sailed over and back. Though in hindsight I think they would have been OK for the crossing on the trip back and I think they regretted not coming.
If you try to make sure that the first experiences are positive -- and limit the negatives (like long passages into the wind) you have a shot at winning over the reluctant cruiser and having them see the light. Some will never take to it off course, but others I think can come to appreciate the beauty of the cruising lifestyle even if they are not die-hard sailors, if you accomodate them by avoiding arduous passages especially at first, and maybe a little more comfortable boat than your would have yourself.
I think you're right. My perception is that many folks think by buying a big tricked out sailboat a passage to the fabulous Caribbean will be nice and easy just like in those magazine articles. They haul their reluctant other on board and after a few jaunts around the bay head out to the Indies. After two weeks of beating to weather and still 800 miles to Grenada, the crew says "no thanks. "
Had these folks opted for a less dramatic (but still fabulous) trip to the Bahamas -- where offshore sailing can be broken into legs avoiding really crappy wx and limited beating, my guess is the dropout rate would have been much less.
Having the right spouse is important, but no less so than a Capt who plans his trip with the capabilities and interest of his crew in mind.