This is extremely long, but I hope it's accurate and enjoyable reading:
When reading, keep in mind:
GVWR = Gross Vehicle Weight Rating. This is basically the weight that the tires of the vehicle are placing on the ground. This is the total weight of the vehicle including passengers, fuel, tongue weight, etc
GCWR = Gross Combined Weight Rating. This is the total weight that your entire rig+trailer+anything else you're dragging behind can be.
Towing capacity is a marketing scam! Tow capacity is determined (by the marketing team) as GCWR minus the total weight of your tow vehicle. This fuzzy math (the marketing team makes it 'fuzzy') is why you go down to the dealer looking for a 3500 and he tries to sell you a 2500 (because he doesn't have the 3500 with the options you want) saying "you know, a 2500 can tow more than a 3500". The reason they claim this is because a 2500 weighs less than a 3500 but has the same GCWR... So, according to the "experts" you can tow a heavier trailer as long as you're below your GCWR.
These jokers are missing one thing... It's called GVWR. GVWR for a 2500 is 8,800 lbs and a 3500 is either 10,500 or 11,000 depending on how it's equipped. Remember, GVWR is the total weight of the vehicle including *everything*. Yes, this everything includes tongue weight!!! Check out the following hypothetical situation:
You have a 10,000lb fifth wheel. You have a '02 Ram 2500 4X4 Quad Cab Long Bed Diesel automatic with a GVWR of 8,800lbs. According to the '02 Ram 2500/3500 book I have in front of me, "For king pin weight multiply by 25%". According to Dodge's recommendation, with our trailer, we need to have 2500lbs of tongue weight for our trailer. Many will keep the king pin weight around 18-22% of the total weight which will still bring us to a tongue weight of between 1,800 and 2,200lbs respectively.
Here's what we have so far:
10,000lb fifth wheel
at least 1,800lbs of king pin weight to be safe going down the road... Dodge recommends in this scenario 2,500lbs, but 1,800 should be the minimum (in my opinion).
Time for more math... Remember, the truck can't exceed 8,800lbs total (GVWR). Wait a minute... we forgot to weigh the truck!!!! Okay, we go to the 'ol CAT scale and toss the old lady in the truck, the dog, can't forget the optional front bumper, optional rear bumper, optional power seats, optional tubular side steps, optional sprayed in bed liner, optional tow hooks, optional diamond plated mud flaps, you get the idea... and to your surprise your truck is a whopping 7,563lbs!!! You say, "holy crap batman, we don't look that heavy". Let's plug in the numbers...
20,000 GCWR
minus
10,000lbs (to make the math simple) wet trailer weight
minus
7,563lbs wet truck weight
equals
2,437
Perfect!!! We're within the GCWR, which means we can cram almost 2,500lbs, more junk into our trailer!!! Woo Hoo! Satellite TV here we come, solar panels here we come, washer/dryer here we come (Employment at the local misinformed stealer here we come). :-laf
Wait a minute! We forgot one thing. What about good 'ol Mr. GVWR? According to this limit, our truck can only weigh 8,800lbs. Ooops. <-Thinking->Hmmm, Let's see, if the truck weighs 7,563lbs and at a minimum my trailer tongue weight should be no less than 1,800lbs... hmmm 7,563+1,800=9363... Holy crap! We're overloaded by 563lbs!!! Sure glad I didn't put in that optional 98gal Transfer Flow tank.
In conclusion, these trucks can pull a lot. With sufficient trailer brakes, they can stop a lot. I'm sure there's a safety margin in there... but in terms of dealer marketing, it's all a scam. Dodge, Ford, and Chevy could bump up the GCWR to 26,000lbs (I believe that's the limit before it's considered medium duty I could be wrong) so there marketing team could bump up the trailer it could tow for commercials. It doesn't matter. If you wrecked pulling a 17,000lb trailer like the marketing might lead you to believe, they can still tell you were overweight in terms of GVWR. Remember one thing (with our light duty trucks especially a 3/4ton) forget the published maximum trailer rating... Unless you're pulling one of those farm wagons that have wheels in the front and don't have any tongue weight on the pintle hook you will exceed GVWR before you get close to GCWR with a properly loaded trailer. One interesting note which I won't get into because this message is long enough is that if you had a tag-along trailer you could be within GVWR and GCWR due to it's lower tongue weight (Dodge recommends 15% per their book but a properly leveled trailer could safely run with 10-12% assuming speed was kept down. The problem is, Dodge also has a rule that any trailer over 10,000lbs is required to be fifth wheel. This is a acceptable rule in my mind... However, one thing is funny. In our above example, our 10,000lb trailer is overloaded with a fifth wheel hitch due to the king pin weight but a 10,000lb tag along is well within the limit. I don't know about you, but I would much rather be next to a "overloaded" fifth wheel rig than a "within the limit" tag-along during an emergency maneuver!!!
Would I be comfortable driving next to most TDR members that are pulling a 25,000lb trailer? *Definitely* Most people that I know that are into their diesel trucks happen to be very safe and "common sense" drivers. It all comes down to common sense. I rather drive next to an experienced driver that is overloaded then an idiot trying to back a 500lb jet ski down the boat ramp a the lake. Experience and common sense make an enjoyable and safe towing combination.
Okay, I'm done.
Attention: TDR Forum Junkies 
I agree with your post on weights, but I am compelled to say that just because your rig will pull it and stop it won't make a hill of beans to some CHP with a portable scale and a chip on his shoulder for RV'ers. The bottom line is do what is in your comfort zone, but beware. If you get Highways magazine from Good Sam, you will see that several states are hot on RV's and being overloaded. Be careful out there... ... ... 
