Nearly all my 1,000 or so freight cars have sprung trucks.
Dave Nelson is correct in that the springs are stiff enough as to not compress under the weight of the cars.
BUT, nearly EVERY HO two axle sprung truck I have ever seen in my 56 years of model railroading does EQUALIZE under the weight of even the lightest cars.
That is why I use them - equalization - keeping all four wheels on the rail ALL THE TIME.
As for what is currently being manufacturered, Kadee is the main thing out there.
I use mostly Kadee trucks but I replace the Kadee plastic axle wheelsets with Intermountain wheelsets.
This creates a heavy, equalizing, and extreamly free rolling truck - allowing my locos to pull about 10%-15% more tonnage than when pulling plastic rigid trucks with metal wheelsets.
The other advantage to my setup is the weight is down low, also helping to improve tracking.
As for the detail issue asked about by the OP, as noted wjstix above, Kadee #555 sprung trucks, which represent 100 ton roler bearing trucks do have three springs.
Prototype trucks of 50 ton or 70 ton ratings do not generally have three outward visable springs.
Nearly every freight car line in the is hobby back in the 50’s and 60’s had sprung trucks - Athearn, Varney, Walthers, Roundhouse, Silver Streak, and many more, had sprung trucks and sold them separately as well.
And brands like Central Valley, Lindberg, Kadee and others also offered sprung trucks even if they were not in the freight car business, or only had a few freight car products.
Central Valley had a very complete line of freight and passenger trucks - all metal - all sprung.

Take careful note of the unassembled truck parts in the box of this late 50’s Athearn plastic kit.
Still doing it the old way here on the ATLANTIC CENTRAL.
Sheldon