It's not really a question about if the vehicle can tow the boat, it's about can it do it legally.
Yea, capacities are no longer marketing hype. SAE J2807 regulates how those ratings are determined and published. I think all the manufacturers have moved to that system to determine their tow ratings at this point.
To those that think the rules do't apply to them.....
Here's a list of what weight ratings are
not
"The engineers throw a ton of safety factor on there, so you'll be fine"
"The tow ratings are all determined by lawyers or the marketing department anyway, there's tons of capacity left"
"I've been doing this for years and I've never had a problem"
Feel free to add whatever cliche answer you would like to give when you justify towing over your vehicles ratings. Be prepared to defend that in a court, and to explain to someone's loved ones when you cause an incident because you thought the rules didn't apply to you.
Here's a great article on why towing within the limits is important.
Now that I'm off my soap box, here's why I choose a tow vehicle with a 9,200lb rating for a 4,000lb trailer:
That is a bed full of "stuff". I'm estimating around 750-1k lbs of "stuff". There are cornhole boards, a baby stroller, suitcases, tools, food, and all the misc "stuff" that we needed for a weeks vacation with a 7yr old and 15mo old baby. The bed was FULL to the top. That takes off my 9,200lb rating.....I'm down to 8,200lbs. Now, I had a 30lb toddler, a 60lb kid a 150lb wife, and another 50lbs of "stuff" in the cab with me. That drops me to 7,910lbs of capacity to tow. I had an additional 200lbs of "stuff" in the boat (kids toys, another cooler with adult beverages, camp chairs, and an easy up. Down to 7,710lbs of capacity. Considering I'm towing at 4,000lb (nominal) trailer that leaves me about 50% (3,710lbs) under my MAXIMUM tow rating. Plenty of headroom so that I'm not over the limit at max load. Every single lb of capacity I can retain over my actual load adds to my safety factor. This safey factor gets eaten into very quickly in heavy traffic, torrential rain downpours, interstate speed, etc. If I'm towing something 400 miles with the 3 most important people in my life enclosed inside, I want as much safety factor as I can get.
For reference, a Silverado/Sierra with the 3.08 rear gears in this body configuration is only rated at 5,200lbs. I would have been OVER the rated limit of that truck with an AR190 and a weeks worth a "stuff". So it's pretty easy to see how you can EASILY go over your rated limit with a 23ft boat, in even something as "large" as a 1500 class pickup. Imagine if you started with a 3,500lb rating in a 2dr jeep, and had a 5,500lb trailer.....you're in the negative before you even get started!