It is all sales hype because Ford is behind Toyota in sales and is
very worried about their new truck. It is not the boxing of the frame
alone that makes it strong but rather the thickness and grade on
metal. They use a thinner rail that is boxed for more stiffness but it
is not really any stronger than old one at yeild point and when a box
frame fails it collapses while a C channel frame tends to flex more
before it yeilds and even then not suddenly like a boxed frame can.
Personally I think their 1/2 ton commercail is a joke fore towing
capacity because it has same LD rear springs as before and no more
power. You tow 11K with that it would realy suck at times power wise
were as the Toyota would walk away from Ford with same load  (and a
Dodge and Chevy too) because it has better power, tranny gears and
axle ratio. This is not pro Toyota and anti Ford but rather it take
more than a "rating" on a commercail to really make it all happen
right. FOrd went 11K becuase Toyta said 10K and some change. If
Toytota had said 12K, Ford would have said 13K. The only problem is
that while 10K is a lot for a 1/2 ton P/U, a Toyota has engine, axle
and tranny to move it very effectively while they other brands do not.
I have drive a New Toyota and it is a beast with lots of power more so
than any other 1/2 ton I have driven and the 6 speed aito worked
flawlessly. If this is any gage as to how they are going to build a
truck, when they roll out and 3/4 and one ton model Detriot is going
to be scrambling to catch up (word is that Toyota is going to have the
option of a CAT diesel in HD 08 P/U's so that they can better woo
buyer of these kinds of trucks)    
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TheSnoMan.com

The front portion of the Super Duty frame is fully boxed. The rear
portion is open C-channel but very heavy. Different applications have
different needs. If you are mounting a fifth wheel hitch, having the
open C-channel is better since the fifth wheel hitch mounts to the
frame near the center of the bed. For a rear receiver, the fully boxed
frame is probably better. However, either design can be made strong.
In the end it comes down to production equipment, design requirements,
and engineering judgment. The fully boxed frame might be the reason
that the F150 can tow 11,000 lbs, but it probably isn't the reason the
Tundra can't. I am sure that you could design an open C-channel frame
with the same rigidity as the fully boxed frame - however it might be
heavier for a given stiffness. For a load carrying truck it is
sometimes desirable to have a frame with a very high shear strength
(think pressing straight down) but with somewhat less torsion rigidity
(think twisting). When you are on uneven surfaces allowing the frame
to twist slightly can reduce peak loads on portions of the frame. The
Ford F150 commercial is too simplistic in that it leads one to believe
that for all conditions one frame design is superior. This is hardly
ever the case. I'd probably guess that for a truckoid like the F150 or
Tundra, the fully boxed frame really is better. For a real work truck
like the F250/350/450, the heavy C-channel rear frame probably has
advantages.

When the current F-150 was introduced I read several articles that
commented (critiqued really) Ford for over engineering the frame. It
was considered too heavy and too expensive for the application. I
guess Ford actually knew what they were doing.  They had enough over
capacity in the design that they were able to just change the
published spec as needed . Toyota designed their truck to beat the
Ford advertised spec, not the actual engineering limit. For most
people who buy a half ton truck, the maximum is irrelevant. If you
really want to tow 10,000 lbs. you'd be stupid to buy a Tundra or an
F150. For the same money as a 1/2 ton truck equipped to tow 10,000,
you can buy an F250 or even an F350.

Ed

You make a good point. It doesn't matter how the frame is made, really, what
matters is how much you can carry. When the heavy duty frame option came out
(3000 lb payload) it effectively made the F250 redundant.  Ford has to be
careful how light they build the F250 for that reason.  If you look at the
old GVWR's and payloads there have always been F250's with a lot less
payload than that.  It's not a bad idea, but it just looks embarrassing, as
you pointed out.

3000 lb is, after all, a ton and a half.  It's overkill for a pickup.